Preheat your oven to 375°F (190°C) and line a large, rimmed baking sheet with parchment paper or a reusable silicone mat. This is the starting point for a perfect batch of zucchini boats, because a stable, nonstick surface makes it easy to slide the fragile boats on and off the pan without breaking them. While the oven heats, rinse four medium zucchini under cool water and dry them thoroughly. Choose squash that are about 7–8 inches long and roughly 2 inches in diameter; these have the ideal ratio of flavorful flesh to sturdy skin. Trim off the stem end, and use a small paring knife to slice a very thin lengthwise sliver from the bottom of each zucchini so they sit flat. If you skip this step, the boats will rock and spill filling while baking. Pat the zucchini dry again, because any surface moisture will turn steam in the oven and make your final dish soggy.

Cut each zucchini in half lengthwise to create eight long halves. Using a sturdy melon baller or a small spoon, scoop out the center flesh, leaving a 1/4-inch (6 mm) wall on the bottom and all around the sides. You want a canoe shape that can hold a generous amount of filling without becoming fragile. Reserve the scooped-out flesh in a bowl and roughly chop it into small pieces; you’ll incorporate it into the beef filling, which adds moisture, fiber, and a gentle summer-squash flavor. To prevent watery boats, place the hollowed zucchini halves cut-side down on a double layer of paper towels and sprinkle the exposed insides with a pinch of kosher salt. Let them sit for at least 10 minutes while you cook the filling. This salting step is a game-changer: it pulls excess water out of the zucchini through osmosis, allowing the flesh to brown and concentrate in flavor rather than boiling in its own juices.

In a large 12-inch skillet, heat 1 tablespoon of olive oil over medium heat. Add the finely chopped yellow onion and sauté for 2 to 3 minutes, stirring frequently, until the onion is translucent and lightly golden at the edges. The sweet, savory aroma of onions cooking in oil is the base of this dish. Add the minced garlic and cook for just 30 seconds, stirring constantly, until fragrant. Do not let the garlic brown more than a light golden tone, because over-cooked garlic becomes acrid and can dominate the Italian herb blend. Next, add the lean ground beef, breaking it into small crumbles with a wooden spoon. Cook for 5 to 7 minutes, stirring occasionally, until the meat is deeply browned and no pink remains. If there is excessive rendered fat, carefully tilt the pan and spoon out all but about 1 tablespoon, or use a paper towel to soak it up. Leaving a tiny bit of fat in the pan keeps the filling moist without becoming greasy.

Now it’s time to build the flavor base. Sprinkle the browned beef with 1 teaspoon of dried Italian herbs, 1/2 teaspoon of fine sea salt, and 1/4 teaspoon of freshly ground black pepper. Add the reserved chopped zucchini flesh and 1/2 cup of crushed tomatoes or jarred marinara sauce. Stir everything together until the zucchini is coated in the tomato-herb mixture. Reduce the heat to medium-low and let the filling simmer gently for 3 to 4 minutes, uncovered. During this time, the zucchini flesh will soften and release its liquid, which will reduce and meld into the sauce. You’ll notice the filling looking tighter and less watery as it cooks. Taste a small spoonful and adjust the seasoning—this is your chance to add a pinch of red pepper flakes, an extra clove of garlic, or a few drops of Worcestershire sauce for umami. Once the filling is thickened and glossy, remove the pan from the heat and set it aside for 2 to 3 minutes to cool slightly. A slightly cooled filling is easier to handle and won’t turn the cheese into a puddle before baking.

Return to the zucchini boats. Turn them cut-side up and pat the cavities dry with a paper towel to remove any accumulated moisture. If you want a touch more richness, brush the inside of each boat with a little olive oil or melted butter—this helps create a tender interior and a nice golden edge. Using a regular tablespoon or a cookie scoop, divide the beef filling evenly among all eight zucchini halves, mounding it slightly above the rim. Don’t be afraid to pack it fairly tightly; the filling will help support the boat structure. Arrange the filled boats side by side on the prepared baking sheet, leaving at least 1/2 inch of space between them so hot air can circulate and crisp the outer surfaces. If the boats are crowded, they will steam and become mushy.

Top each filled boat generously with shredded part-skim mozzarella and a sprinkle of grated Parmesan. A good ratio is about 1 level tablespoon of mozzarella plus a teaspoon of Parmesan per boat, but if you’re a cheese lover feel free to add a little extra—just make sure the cheese is spread evenly so it melts and browns in patches rather than sliding off in one solid layer. For an extra layer of flavor, add a tiny pinch of dried oregano or red pepper flakes over the cheese. Transfer the baking sheet to the middle rack of the preheated oven and bake for 15–18 minutes, or until the zucchini is fork-tender, the filling is hot and bubbling, and the cheese is fully melted with golden-brown spots. If you prefer a more browned top, switch the oven to broil for the last 1–2 minutes and watch carefully to prevent burning.

When the boats are perfectly baked, remove the baking sheet from the oven and let them rest for 3 to 5 minutes on top of the stove or a cooling rack. This resting period is not just for patience—it allows the juices to settle and lets the cheese set slightly, so the first bite doesn’t burn your tongue and the filling stays intact when you lift a boat. Garnish with a shower of freshly chopped parsley or basil and a light drizzle of extra-virgin olive oil if you like. The zucchini should be easily pierced with a fork but still hold its shape when lifted. Serve the boats warm, perhaps with a simple green salad or a side of cauliflower rice to keep things low-carb and filling.

Leftover zucchini boats can be stored in an airtight container in the refrigerator for up to 3 days. Reheat them gently in a 350°F (175°C) oven for 8–10 minutes, or microwave a single boat at 70% power for 90 seconds to 2 minutes. The texture of the zucchini will soften upon reheating, but the flavors will actually deepen overnight. To meal prep, assemble the boats completely but stop short of baking; cover the tray tightly with plastic wrap and refrigerate for up to 24 hours, then bake when ready. You can also freeze unbaked boats by wrapping each one individually in plastic wrap and then aluminum foil; frozen boats can be baked at 375°F for 25–30 minutes, no need to thaw, and are perfect for busy weeknights. Add five minutes to the bake time if going from frozen.