In a small bowl, combine yogurt, lemon juice, 1 clove garlic, and 1/4 teaspoon salt. Set aside.
Combine ground beef, oregano, 3/4 teaspoon salt, 1 clove garlic, and cayenne pepper in a medium-size bowl. Mix well. Form beef mixture into 24 meatballs about 1-inch in diameter. Place meatballs in a 15x10x1-inch baking pan.
Bake meatballs, uncovered, for 20 minutes, or until no longer pink.
Carefully open pita bread halves. Line each half with a lettuce leaf. Fill each half with 3 meatballs, 1 tablespoon of sauce, and tomato wedges.