Preheat grill to high + oil grates; cut off the stem of 1 onion, discard outer skin, then carefully slice onion into ¼ to ½-inch rounds; drizzle with oil + salt/pep; grill 5 min with lid closed, flip + grill 4-6 min until charred + slightly softened

Meanwhile, rub steaks with 1 tbsp oil + salt/pep; grill 2-5 min with lid closed, flip + grill 3-4 min more until charred + cooked through; rest 5 min + thinly slice

Grill 2 crust until warm + toasted; spread half the tzatziki onto then crust, then top with grilled steak + onions—that looks amazing!