Preheat the oven to 375 degrees F. Spray a 9 x 13 inch baking dish with non-stick spray. Spoon 1 cup of the spaghetti sauce into the baking dish and spread to coat the bottom. Set aside.
Cook jumbo shells to al dente. Whisk the egg in a large mixing bowl. Add the ricotta cheese, 2 cups mozzarella cheese, ¼ cup Parmesan cheese, Italian seasoning, salt and black pepper until combined.
Place the shells seam side up in the prepared baking dish. Pour remaining sauce over shells. Top with 1 cup Mozzarella cheese and 1/4 cup parmesan cheese.
Cover the pan with foil and place in a preheated oven at 375 degrees F. Bake for 30 minutes, uncover the baking dish and broil on high for 2-4 minutes or until the cheese is golden brown.