Preheat the Oven: Start by setting your oven to 375°F (190°C).

Cook the Sausage: In a large skillet, heat olive oil over medium heat. Add the Italian sausage and cook until browned, about 5–7 minutes. Remove from heat.

Combine the Vegetables: In a large mixing bowl, toss together sliced potatoes, onion, minced garlic, sliced bell pepper, undrained diced tomatoes, Italian seasoning, salt, and pepper.

Layer the Casserole: Grease a baking dish and layer half of the potato mixture on the bottom. Add half of the cooked sausage, followed by half of the shredded mozzarella cheese.

Repeat Layers: Add the remaining potato mixture and sausage, finishing with the rest of the mozzarella cheese on top.

Bake the Casserole: Cover with foil and bake for 45 minutes, then uncover and bake for an additional 15–20 minutes.

Garnish and Serve: Remove from oven and sprinkle with fresh parsley before serving.