Preheat oven to 350 degrees. Spray 9 x 13 baking dish with non-stick cooking spray.
Cook pasta per directions on back of package for al dente. Drain pasta and put back into pot.
While pasta is cooking, in a large skillet heat up cooking oil. Add onion, bell pepper, and sausage. Cook until sausage is browned and onions and peppers are tender. Add in garlic and cook for 1 minute. Turn off burner.
Add cooked sausage, jars of pasta sauce, Italian seasoning and 1 cup of mozzarella cheese to the drained pasta in the pot. Stir to combine.
Pour mixture into a prepared 9x13 baking dish evenly. Sprinkle rest of 2 cups mozzarella cheese over casserole. Place pepperoni evenly over cheese. Bake for 20-25 minutes until cheese is bubbly and pepperoni is crisp.
