– 1 lb 80/20 ground beef or ground turkey – 1 tsp salt – ½ tsp ground black pepper – ¼ (1 oz.) red onion, finely chopped – 1 fresh jalapeño, cut in small piece – 1 (4 oz.) tomato, thinly sliced – 1 (7 oz.) avocado, cut lengthwise – 1 butterhead lettuce – 8 slices cheddar cheese – 1½ oz. butter, in slice