Lettuce Tuna Tacos

Ingredients:

• 2½ oz. tuna steak
• 1 tbsp. taco seasoning
• 2 tbsp. cilantro
• ¼ cup tomatoes
• 1½ tbsp. butter
• 1½ tbsp. sour cream
• Lime wedge
• 3/4 oz. red onion
• ¼ avocado
• 6 romaine lettuce leaves