Preheat oven to 350 degrees.
Cook rotini according to package directions. Set aside.
Meanwhile, cook and stir ground beef and onion in large skillet over medium high heat until meat is no longer pink. Season with salt and pepper.
Combine rotini, pizza sauce, tomato sauce, tomato paste, sugar, garlic salt and oregano in large bowl. Add beef mixture, stir until blended.
Plave half of mixture in 3 quart casserole, top with 1 cup cheese. Repeat layers. Arrange pepperoni slices on top. Bake 25 to 30 minutes or until heated through and cheese is melted.
