In a large skillet, cook ground beef and onion over medium-high heat until browned, stirring frequently. Drain and return beef mixture to skillet; stir in soup. Reduce heat to medium; bring to a boil, stirring occasionally.
Spoon beef mixture into an 8"x8" baking pan lightly sprayed with non-stick vegetable spray. Spoon pizza sauce evenly over beef mixture; arrange pepperoni and green pepper over sauce. Sprinkle with cheese; arrange potato puffs over top.
Cover with aluminum foil; bake at 375° for 30 minutes. Uncover; bake an additional 15 to 20 minutes, until heated through.