Preheat Your Oven'S Broiler. In A Medium Bowl, Stir Together The Onion, Tomato, Celery, Bell Pepper, Cheese, Chili Powder And Salt. Arrange Slices Of Bread On A Baking Sheet Or Broiling Pan. Top Each One With 1/4 Of The Mixture, Spreading Out To The Edges. Broil For 4 To 5 Minutes, Or Until Cheese Melts. Watch Closely To Prevent Burning. Serve Immediately.