How to Make It
Preheat broiler with oven rack 6 inches from heat. Place ground chuck, feta cheese, oregano, parsley, crushed red pepper, egg, 1 teaspoon of the salt, and 1/2 teaspoon of the pepper in large bowl, and gently combine.
Shape mixture into 32 meatballs, and place on a large aluminum foil-lined rimmed baking sheet. Broil until meatballs are no longer pink in centers, 8 to 10 minutes.
Meanwhile, stir together yogurt, cucumber, mint, dill, lemon zest, lemon juice, and remaining 1 teaspoon salt and 1/2 teaspoon pepper in a bowl.
Reserve 12 meatballs and 1 cup cucumber-yogurt sauce for stuffed pitas (see below). Serve remaining meatballs and cucumber-yogurt sauce with hot cooked rice.
Reheat 12 meatballs; stuff 3 meatballs into each of 4 warm pita bread halves. Add lettuce, tomato, and red onion; top with 1 cup cucumber-yogurt sauce.