In large bowl, mix meat, catsup, instant minced onion, salt, pepper, celery seed, and garlic powder. Shape mixture into 16 thin patties; chill. Mix vinegar, oil, and dillweed. Place onion slices in shallow glass dish; pour vinegar mixture over onions. Cover; refrigerate at least

30 minutes. Wrap rye bread in a single thickness heavy-duty aluminum foil. Place on grill 4 inches from medium coals. Heat 20 minutes, turning occasionally. Remove onions from marinade; reserve marinade. Place hamburgers on grill 4 inches from medium coals. Cook 5 minutes on each side or until done, brushing frequently with reserved marinade. To serve, place 1 hamburger patty on slice warm bread; top with onions, a second patty and a second slice bread. Makes 8 servings.