Slice the bell peppers into strips, chop the onion, and mince the garlic. Cut the Italian sausage into bite-sized pieces.

In a large skillet, heat olive oil over medium heat and cook the sausage until browned.

Sauté the bell peppers and onion in the same skillet until softened, then add the garlic.

Combine the sausage with the sautéed vegetables, crushed tomatoes, herbs, salt, and pepper; simmer.

Preheat the oven to 375°F (190°C) and transfer to a baking dish if skillet isn't oven-safe. Bake with Parmesan cheese on top.

Garnish with parsley or basil before serving.