Add 1-2 T. olive oil to fajita skillet. Slice whole onion in half, pole to pole. Rub olive oil all over onion. Place onion halves cut side down in skillet. Cover with foil with ends tucked securely under skillet.

Preheat grill to 350 degrees, using only one side of the burners. Once temperature is reached, place onions on the cool side away from the flames.

Steam/bake onions for about 45 minutes-1 hour. Lower flame to medium and move skillet/onions to hotter side of grill. Grill until desired char is reached, turning every 5-10 minutes.