- Preheat oven to 350°F.
- Prepare pasta according to package directions, reducing boiling time to 8 minutes.
- Cook sausage, peppers, onion, and garlic in hot oil in a 12-inch cast-iron skillet over medium-high, stirring often, until vegetables are soft and sausage has begun to brown slightly, 7 to 8 minutes.
- Stir in tomatoes, tomato sauce, sugar, salt, and pepper. Bring mixture to a simmer over medium, and add 1/2 cup of the Parmesan, stirring until melted.
- Stir in cooked pasta.
- Remove from heat, and sprinkle with mozzarella and remaining 1/4 cup Parmesan.
- Bake in preheated oven until mixture is bubbly and cheese is golden, 25 to 30 minutes.
- Let stand 10 minutes before serving.