Prepare charcoal grill for direct-heat cooking.

In medium-size bowl combine turkey, oats, egg, garlic powder and pepper. Divide turkey mixture in half. On 2 pieces (each 10-X 11-inch) wax paper, shape each half of turkey mixture into a 6-inch diameter circle.

Sprinkle onions and relish over one circle of turkey mixture, leaving a 1/2-inch border around outside edges; top with catsup and mustard. Cut cheese into 4 equal strips and arrange cheese strips, spoke-fashion, over catsup and mustard. Carefully place remaining turkey mixture circle on top of cheese. Remove top layer of wax paper from turkey mixture. Press turkey mixture edges together to seal.

Lightly grease cold grill rack and position over hot coals. Invert giant burger onto grill rack; remove wax paper. Grill burger 8 minutes per side or until internal temperature of 165 degrees F. is reached on meat thermometer. To turn burger, slide a flat cookie sheet under burger and invert onto another flat cookie sheet, then slide back onto grill rack*.

To serve, cut burger into fourths. Serve with lettuce and tomato slices if desired. * Can also use greased grill basket if desired.