Mix together bread crumbs, onion and the 1/4 cup water. Let stand until water is absorbed by breadcrumbs.
Add the ground beef, salt and beaten egg and combine well. Form into meatballs about the size of a marshmallow (about 1.5-inches diameter).
Heat oil in a large skillet over medium heat. Brown meatballs on all sides, carefully turning them so they don't fall apart and are completely cooked. Remove from pan; set aside.
In the same skillet, saute the celery and bell peppers until crisp-tender; about 5 minutes.
Add the brown sugar, cider vinegar, pineapple and water/pineapple juice mixture. Heat till boiling.
Mix the thickener ingredients and add to the boiling sauce. Stir until thickened, reduce heat and cook for 1 minute.
Add meatballs back to pan and stir to coat them with sauce and heat through.