Preheat oven to 375 °F (190 °C).
Slice zucchini lengthwise and scoop out seeds and flesh to create hollow boats.
Heat olive oil in a skillet over medium heat.
Add chopped onion and diced bell pepper; cook until softened.
Stir in minced garlic and cook for 30 seconds.
Add ground meat, breaking it up with a spoon, and cook until browned.
Season with Italian seasoning, salt, and black pepper.
Stir in marinara sauce and simmer for a few minutes.
Place zucchini boats in a baking dish and spoon the meat mixture evenly into each.
Sprinkle shredded mozzarella and grated Parmesan over the zucchini.
Bake for 20–25 minutes until zucchini is tender and cheese is melted and golden.
Garnish with fresh parsley or basil if desired and serve warm.