Brush the cooking grates clean. Brush the onion slices on both sides with oil, and then grill over direct medium-highheat, with the lid closed, until charred and caramelized on both sides, 6 to 8 minutes, turning once or twice. At the same time, grill the patties over direct medium-high heat, with the lid closed, until cooked to medium doneness, 8 to 10 minutes, turning once. During the last 30 seconds of grilling time, toast the buns, cut side down, over direct heat.
Brush the cooking grates clean. Brush the onion slices on both sides with oil, and then grill over direct medium-highheat, with the lid closed, until charred and caramelized on both sides, 6 to 8 minutes, turning once or twice. At the same time, grill the patties over medium-high heat, with the lid closed, until cooked to medium doneness, 8 to 10 minutes, turning once. During the last 30 seconds of grilling time, toast the buns, cut side down, over direct heat.