Simply mix the yogurt, relish, lemon juice, lemon zest, salt, and black pepper until well-combined. Set aside.
For the burgers:
In a large bowl, combine the ground turkey, finely diced red onions, finely chopped parsley, whisked egg, crumbled feta cheese, chopped sundried tomatoes, minced garlic, salt, and black pepper.
Form the mixture into four flat patties.
In a large skillet over medium heat, heat up the olive oil for 1-2 minutes. Add in the patties and cook until golden brown and fully cooked through, about 5-6 minutes per side.
Serve on a bun with the relish sauce and desired toppings.