Lamb Burgers with Mint Pesto and Whipped Feta

Name: Lamb Burgers with Mint Pesto and Whipped Feta
Ingredients: For the mint pesto and whipped feta:; 2 packed cups fresh mint leaves; 1/4 cup blanched slivered almonds; 1/3 cup finely grated Parmesan cheese, or to taste; 1 large garlic clove, minced (optional); 1/3 cup olive oil (not extra virgin); Salt and black pepper to taste; 8 ounces feta cheese, at room temperature; 4 ounces cream cheese, at room temperature; Zest of 1 lemon, finely grated; For the burgers:; 2 pounds ground lamb; 6 hamburger buns; 6 leaves butter lettuce (optional)