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Extreme close-up view of the top of the cheesy Italian sausage and bell pepper casserole.

Cheesy Italian Sausage and Bell Pepper Casserole

This casserole is packed with Italian sausage, tender bell peppers and onions, and, of course, lots of melty mozzarella cheese! It's super quick to throw together, and the recipe is super low carb and keto, too. Our whole family loves it - even the kids.
Course Main Course
Cuisine Italian
Keyword low carb, meal prep, one-pan meal
Prep Time 15 minutes
Cook Time 1 hour
Total Time 1 hour 15 minutes
Servings 8 servings
Calories 408kcal


  • 9x13 baking dish
  • Cooking spray
  • Large skillet
  • Small bowl
  • Large bowl (or use the skillet if it's large enough)
  • Aluminum Foil


  • 1 ½ pounds Italian sausage link or rope sausage
  • ¼ cup tomato paste
  • ¼ cup water
  • 2 teaspoons Italian seasoning
  • 4 large bell peppers various colors; seeds removed, sliced into ½-inch-long pieces
  • 1 medium onion halved, sliced into ½-inch-long pieces
  • 2 cups freshly shredded mozzarella divided
  • ½ teaspoon salt
  • fresh basil chopped or chiffonaded; for garnish


  • Preheat oven to 375° Fahrenheit. Spray 9x13 baking dish with cooking spray and set aside. Cut sausage into 1-inch pieces.
  • Heat large skillet over medium heat, then add sausage. Cook 10 minutes or so, stirring occasionally, until sausage is browned but not fully cooked through. Drain any liquid from skillet.
  • In small bowl, whisk together tomato paste, water, and Italian seasoning, stirring until well combined. Set aside.
  • In large bowl (or skillet if large enough), mix together browned sausage, bell peppers, and onions. Pour tomato sauce over sausage and vegetables, then stir well to coat thoroughly.
  • Transfer half of sausage mixture to greased baking dish. Top with 1 cup mozzarella. Spread remaining sausage mixture on top of cheese and cover baking dish with foil.
  • Place covered baking dish in preheated oven and bake 30 minutes. After 30 minutes, remove foil and stir casserole well. Top with remaining 1 cup mozzarella and return baking dish to oven, uncovered.
  • Bake, uncovered, 10 minutes or until sausage is no longer pink and peppers are tender. Remove from oven and serve hot.


  • Mozzarella: Shred your own mozzarella from a block of fresh cheese. It melts much better than the pre-shredded version, and it doesn't contain any added fillers or anti-clumping agents (especially important if you're low carb or keto!).
  • Make it Keto: Be sure your tomato paste doesn't contain any added sugars or any sugar substitutes that aren't keto-friendly. Natural sugars from the tomatoes are fine. You also want to make sure the sausage doesn't contain any sugar and has the fewest carbs possible. Use all green bell peppers rather than a variety of colors; green bell peppers have the fewest carbs.


Serving: 1serving | Calories: 408kcal | Carbohydrates: 8g | Protein: 19g | Fat: 33g | Saturated Fat: 13g | Polyunsaturated Fat: 4g | Monounsaturated Fat: 14g | Trans Fat: 1g | Cholesterol: 87mg | Sodium: 951mg | Potassium: 406mg | Fiber: 2g | Sugar: 4g | Vitamin A: 501IU | Vitamin C: 69mg | Calcium: 179mg | Iron: 2mg | Net Carbs: 6g