with Cucumber Dill Sauce
In medium bowl, combine 6 tablespoons yogurt, sour cream, cucumbers, 2 tablespoons feta, 1 teaspoon dill, and ½ teaspoon garlic; salt and pepper to taste. Set aside.
In large bowl, combine ground turkey, mushrooms, spinach, egg, remaining 2 tablespoons yogurt, 6 tablespoons feta, 2 teaspoons dill and 1 teaspoon garlic; salt and pepper to taste. Gently mix until just combined. Form into 12 patties.
Spray a large skillet with cooking spray. Place over medium-high heat; when hot add patties, in batches if needed. Cook, turning once, until internal temperature reaches 170°F on an instant read thermometer (about 8 minutes).
Spread buns with Cucumber Dill Sauce. Top with lettuce, tomatoes, onions and turkey burgers.