Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
Slice each zucchini in half lengthwise. Use a spoon to scoop out the center, leaving a small border around the edges. Set aside the scooped flesh.
Place the hollowed zucchini halves on the baking sheet, brush with olive oil, and bake for 10 minutes to soften slightly.
While the zucchini bakes, heat a skillet over medium heat. Add a drizzle of olive oil, then sauté onion and garlic for 2 minutes until fragrant.
Add the ground chicken and cook until browned, breaking it apart as it cooks.
Stir in the diced bell pepper, tomatoes, and chopped zucchini flesh. Cook for 5–7 minutes until the vegetables soften.
Add Italian seasoning, salt, and pepper, then remove from heat. Stir in half the mozzarella and half the Parmesan.
Spoon the chicken mixture into the pre-baked zucchini halves. Top with the remaining cheeses.
Return to the oven and bake for 12–15 minutes, until the cheese is melted and lightly golden.
Sprinkle with chopped parsley before serving.
