Best Pizza Casserole Recipe - How to Make Easy Pizza Casserole

Ingredients

• 4 tbsp. extra-virgin olive oil, divided, plus more for pan
• 12 oz. cavatappi pasta
• 2 tbsp. plus 2 tsp. kosher salt, divided
• 1 lb. Italian sausage, casings removed
• 8 oz. cremini mushrooms, stemmed and sliced
• 1 small yellow onion, chopped (about 1 1/2 c.)
• 2 cloves garlic, finely chopped
• 3 (8-oz.) cans tomato sauce
• 1 (14.5-oz.) can diced tomatoes
• 1 1/2 tsp. dried oregano
• 1 tsp. dried basil
• 1/4 tsp. crushed red pepper flakes
• 1/2 green bell pepper, seeds and stem removed, chopped into 1/2" pieces
• 3 c. shredded mozzarella, divided
• 1/3 c. sliced pepperoni (about 2 oz.)