Peel and cut onion into four 1/4-inch-thick slices; reserve remaining onion for another use. Shape meat loosely into four 1/2-inch-thick patties; sprinkle with garlic powder, salt, and pepper. Press 1 onion slice into the center of each patty and shape meat around onion until top of onion is flush with the surface of the meat patty.

For a charcoal grill: Place patties, onion side up, on the rack of an uncovered grill directly over medium coals. Grill for 10 to 13 minutes or until meat is done (160 degrees F), carefully turning once halfway through grilling with a spatula. Lightly brush kale leaves with oil and add to grill the last 1 to 1-1/2 minutes of grilling. For a gas grill: Preheat grill. Reduce heat to medium. Place patties, onion side up, on grill rack over heat. Cover and grill as above. Lightly brush kale leaves with oil and add to grill the last 1 to 1-1/2 minutes of grilling.

To serve, place 2 kale leaves on each bread slice. Top with a slice of cheese, then the meat patty, onion side up. Makes 4 servings.

Start the burgers onion-side-up to ensure the onion is nestled securely in the meat. Even when the ground beef firms up, turn carefully to keep onions intact.