Prepare Zippy Corn Relish; cover and chill until ready to serve.
Combine ground round and chili powder, mixing well. Shape mixture into 6 (1/2-inch-thick) patties.
Coat grill rack with cooking spray; place on grill over medium-hot coals (350° to 400°). Place meat patties on rack; grill, covered, 4 minutes on each side or until done. Grill bun halves, cut sides down, 1 minute or just until toasted, if desired.
To serve, line bottom half of each bun with 1 lettuce leaf; top with 2 tomato slices and a meat patty. Top each patty with 2 tablespoons salsa and 2 tablespoons Zippy Corn Relish. Reserve remaining corn relish for other uses. Top with remaining bun halves.