Preheat the oven to 375°F.
Slice zucchini in half lengthwise and scoop out seeds and some flesh to form boats.
Heat olive oil in a skillet over medium heat.
Cook chopped onion and diced bell pepper in the skillet until softened.
Add 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 pepper.
Stir in marinara sauce and simmer for a few minutes.
Place zucchini boats in a baking dish and fill each with the meat mixture.
Top with shredded mozzarella and grated Parmesan cheeses.
Bake for 20 to 25 minutes until zucchini is tender and cheese is melted and golden.
Garnish with fresh parsley or basil if desired and serve warm.