In a large mixing bowl, stir spinach, cottage cheese, 1/2 cup mozzarella cheese, egg, red bell pepper, and salad dressing mix until blended.
Stuff each shell with 1 heaping tablespoon of spinach mixture.
Spread half of the spaghetti sauce into a 13x9 inch baking dish.
Place stuffed shells in the dish; spoon the rest of the sauce over the shells.
Sprinkle evenly with the remaining cheese.
Cover with foil.
Bake at 400 degrees for 30-40 minutes or until well heated.
