Rinse chicken breasts; pat dry. Lay chicken in a 12- by 16-inch baking pan. Sprinkle lightly on both sides with kosher salt, onion powder, and garlic powder.
Place chicken on an oiled grill over a solid bed of hot coals or high heat on a gas grill (you can hold your hand at grill level only 2 to 3 seconds); close lid on gas grill. Cook chicken, turning once, until no longer pink in center of thickest part (cut to test), about 10 minutes total for a 6-ounce breast half. Cool and cut into about 1/2-inch chunks. Cover and chill up to 1 day.