Browning the sausage meat in a large skillet over medium-high heat, about 8 minutes, breaking it up into small pieces. Add half the Italian seasoning, salt and pepper.
While the meat is cooking, add the chopped tomatoes and tomato paste to a small saucepan over medium heat. Add the remaining Italian seasoning, plus salt and pepper. Simmer for about 10 minutes, or until slightly reduced.
Add the remaining ingredients (mushroom, onion, bell pepper, pepperoni, and half the cheese) to a casserole dish. When the sausage is done, add it to the mix. Then add the tomato sauce over the top and stir it all up. Sprinkle the remaining mozzarella cheese over the top.
The information shown is an estimate provided by an online nutrition calculator. It should not be considered a substitute for a professional nutritionist’s advice.