prepare pita crumbs in 350 degree oven and cook until dry. roll with rolling pin to make crumbs. in a saucepan, saute onions, green pepper and celery in oil for 2 minutes. add tomatoe sauce and simmer for 10 minutes. Meanwhile prepare meatballs, by mixing beef, grated onion, crumbs, egg, salt and pepper. shape into small balls. Broil until slightly brown. Add meatballs to the sauce and simmer for 30 minutes. serve inside pita pockets.