Halve zucchinis, scoop out centers, and chop flesh.
Arrange zucchinis in baking dish, drizzle with 1 tbsp olive oil, and season.
Cook onion, garlic, and bell pepper; add chopped zucchini flesh. Add beef and cook until browned. Stir in tomatoes, tomato paste, herbs, and seasonings; simmer 5 mins.
Fill zucchini shells with beef mixture, top with cheeses, and bake 20–25 mins until golden. Garnish with parsley or basil before serving.
Notes
For a vegetarian version, substitute ground beef with lentils or mushrooms.