In a medium pot with boiling salted water cook macaroni pasta until al dente. Drain.
In a large skillet cook hamburger and onion until brown. Drain grease. Add mayonnaise and spaghetti sauce; mix well. Add drained and cooked macaroni, cook on medium heat stirring occasionally until heated through. Mix thoroughly.
To serve, pour mixture into a large serving bowl and top with shredded Cheddar cheese. Serve warm.
