Preheat oven to 375°F. In large bowl, combine ground turkey, 1½ tablespoons yogurt, mushrooms, 3 tablespoons feta cheese, egg, 1 tablespoon Spinach & Herb Seasoning and 1 teaspoon Garlic Garlic Seasoning; salt and pepper as desired. Gently mix until just combined.
Form into 24 meatballs; place on a greased baking sheet. Bake 16-18 minutes or until internal temperature reaches 165°F on an instant-read food thermometer.
Meanwhile, in medium bowl, combine remaining ½ cup yogurt, sour cream, cucumbers, remaining 3 tablespoons feta cheese, remaining ½ teaspoon Spinach & Herb Seasoning and remaining ½ teaspoon Garlic Garlic Seasoning; salt and pepper as desired.
Place meatballs in pitas with tomatoes, onions and cucumber sauce.