Prep the oven and pan. Preheat your oven to 400°F (200°C).
Lightly grease a 9x13-inch baking dish with olive oil or nonstick spray.
Hollow the zucchini. Trim the ends, then slice each zucchini lengthwise. Use a spoon to scoop out the center, leaving about 1/4 inch of flesh to create a sturdy “boat.” Chop the scooped flesh and set it aside for the filling.
Par-bake the boats. Arrange zucchini halves cut-side up in the baking dish. Sprinkle lightly with salt.
Bake for 8–10 minutes to soften slightly. This prevents soggy boats and ensures they cook evenly with the filling.
Sauté the aromatics. While the zucchini bakes, heat 1 tablespoon olive oil in a large skillet over medium heat. Add the onion and cook 3–4 minutes until translucent.
Stir in the garlic and cook 30 seconds, until fragrant.
Cook the chicken. Add ground chicken to the skillet. Season with 1/2 teaspoon salt and 1/4 teaspoon black pepper. Cook, breaking it up with a spoon, until no longer pink, about 5–7 minutes.
Build the Italian flavor. Stir in the chopped zucchini flesh, diced tomatoes, tomato paste, oregano, basil, and red pepper flakes if using.
Simmer for 3–4 minutes to thicken slightly and concentrate the flavors. Taste and adjust salt and pepper as needed. For brightness, add a pinch of lemon zest.
Fill the boats. Remove the par-baked zucchini from the oven.
Spoon the chicken mixture evenly into each boat, packing it in gently so it doesn’t spill over.
Add cheese and bake. Sprinkle mozzarella and Parmesan over the top. Return to the oven and bake 10–12 minutes, until the zucchini is tender and the cheese is melted and lightly golden.
Finish and serve. Let the boats rest for 5 minutes so the filling sets. Sprinkle with fresh parsley or basil.
Serve warm with a side salad or a scoop of quinoa for extra staying power.