Greek Turkey Burgers with Tzatziki Sauce

Ingredients

• 1 pound ground turkey
• 1 egg, whisked
• 1 tablespoon red wine vinegar
• ¾ cup low-fat plain Greek yogurt
• 1 teaspoon dried oregano
• ¼ cup red onion, minced
• Pinch of kosher salt and freshly ground black pepper
• ½ cucumber, halved with skin and seeds removed
• ⅓ cup sun-dried tomatoes, chopped
• 1 tablespoon olive oil
• 2 cloves garlic, pressed or minced
• Bibb lettuce leaves
• 4 soft whole-wheat hamburger buns
• 1 tablespoon fresh dill, minced
• ¼ cup feta cheese, crumbled
• ½ cup fresh spinach leaves, chopped
• ½ teaspoon each Kosher salt and freshly ground black pepper