Lettuce Burger With Feta Cheese & Pesto

Ingredients:

3 oz. ground beef
2 tbsp. red onion
1 tsp. basil pesto
½ tsp. garlic
2 slices tomato
¼ tsp. ground cumin
1 tbsp. feta cheese
½ tbsp. butter
1 tbsp. sour cream
1 large lettuce leaf