Prep the oven and pan: Preheat your oven to 400°F (200°C).
Lightly grease a 9x13-inch baking dish or line it with parchment for easy cleanup.
Hollow the zucchini: Slice each zucchini lengthwise. Use a spoon to scoop out the centers, leaving about 1/4 inch of flesh to form “boats.” Reserve about 1/2 cup of the chopped zucchini flesh; finely chop it and set aside. Lightly brush the boats with 1 tablespoon olive oil and season with salt and pepper.
Par-bake the boats: Place the zucchini cut side up in the baking dish.
Bake for 10 minutes to soften slightly. This helps them cook evenly and not water down your filling.
Sauté aromatics: While the zucchini bakes, heat the remaining 1 tablespoon olive oil in a large skillet over medium heat. Add onion and cook 3–4 minutes until translucent.
Stir in garlic and the reserved chopped zucchini flesh; cook 1–2 minutes until fragrant.
Cook the chicken: Add ground chicken, breaking it up with a spoon. Season with Italian seasoning, red pepper flakes (if using), salt, and pepper. Cook 5–7 minutes until no longer pink and lightly browned.
Add marinara: Pour in the marinara sauce and simmer 2–3 minutes to thicken slightly.
Taste and adjust seasoning. You want a savory, well-seasoned mixture that’s not runny.
Fill the boats: Remove zucchini from the oven. Spoon the chicken mixture into each boat, packing it in so it mounds slightly.
Top with cheese: Sprinkle mozzarella evenly over the boats, then dust with Parmesan.
Don’t overdo it—just enough to cover.
Bake: Return to the oven and bake 12–15 minutes, until the zucchini is tender and the cheese is melted.
Broil for color: Switch the oven to broil for 1–2 minutes to brown the cheese. Watch closely to prevent burning.
Finish and serve: Let cool 5 minutes. Garnish with fresh basil or parsley.
Add a light drizzle of balsamic glaze if you like a sweet-savory pop.