Cut zucchinis in half lengthwise and spoon out the seeds, being careful not to go through to the skin. Place zucchini flesh in a bowl; mix in diced tomatoes, white onion, and green pepper.

Heat butter in a skillet over medium heat. Add garlic and sauté until fragrant, about 30 seconds. Add the zucchini pulp mixture. Sauté until almost tender, about 5 minutes. Stir in sausage, Italian seasoning, salt, and pepper.

Let mixture simmer for about 5 minutes; add the tomato sauce. Simmer for 5 minutes more, then reduce heat to low.

Meanwhile, preheat the oven to 350 degrees F (175 degrees C). Bring a pot of water on the stove to a boil.

Place the zucchini halves in the boiling water for 3 minutes. Remove the zucchini.

Place zucchini halves into an oven-safe baking dish. Fill the pieces with your sausage mixture. Top them off with mozzarella and Parmesan cheeses. Cover with foil.

Bake in the preheated oven for 20 minutes. Remove the aluminum foil. Continue to cook until tender, about 30 minutes more.

Garnish with fresh parsley and enjoy!