Brown beef over medium heat. Season browned beef with salt and pepper. Slowly pour tomato sauce(or puree) into pan with browned beef and stir. (If using tomato puree turn up heat slightly and let simmer for about 5 minutes,then taste to see if it tastes more like tomato sauce, if not let simmer for longer covered) Add elbows pasta, chopped onions,water and stir. Let simmer for 20 minutes checking and stiring every 5 minutes to prevent burning on bottom of pan. You may have to add more water while cooking. When pasta is halfway done add seasoning to taste and let simmer, still stirring every 5 minutes for the remaining cooking time. When pasta is cooked and tender and chopped onions are transparent turn heat off and add the cubed cheese. Let cheese melt in pan covered, then serve.