Cook pasta; drain. Cook hamburger; drain fat. In a bowl, mix cottage cheese, butter, tomato sauce, mushrooms, green pepper, oregano, salt and pepper. Place cooked pasta on bottom of a greased 9 x 13-inch pan. Cover with hamburger. Sprinkle with half of mozzarella cheese. Top with half of the pepperoni. Pour tomato sauce mixture evenly over top. Cover with rest of mozzarella cheese. Layer with rest of pepperoni. Bake at 350° for 45 minutes.