Preheat oven to 375° Fahrenheit. Spray a 9×13 baking dish with cooking spray and set this aside. Cut the sausage into 1-inch pieces.
Heat a large skillet over a medium heat, then add the sausage. Cook for 10 minutes or so, stirring occasionally, until the sausage is browned but not fully cooked through. Drain any liquid from the skillet.
Then, in a small bowl, whisk together the tomato paste, water, and Italian seasoning; stirring until well combined. Set this aside.
Next, in a large bowl (or a skillet if it is large enough), mix together the browned sausage, bell peppers, and onions. Pour the tomato sauce over the sausage and vegetables, stirring well to coat thoroughly.
Transfer half of the sausage mixture to the greased baking dish.
Top this with 1 cup of mozzarella.
Now, spread the remaining sausage mixture on top of the cheese.
Cover the baking dish with foil, and place the covered baking dish in the preheated oven. Bake for 30 minutes.
After 30 minutes, remove the foil and stir the casserole well. Top it with the remaining 1 cup of mozzarella and return the baking dish to the oven, uncovered.
Bake uncovered for 10 minutes, or until the sausage is no longer pink and the peppers are tender. Remove from the oven, serve it hot, and enjoy!
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!