Greek Yogurt Sauce: In a small bowl, mix all sauce ingredients. Place in the fridge to chill.
Preparation: Preheat oven to 425°F (220°C). In a large bowl, combine all burger ingredients except oil. Mix well and form into patties.
Cooking: Heat olive oil in a large frying pan over medium heat. Sear burgers for about 2 minutes per side, until golden brown. Transfer to a baking sheet and bake for 7-10 minutes, or until cooked through.
Tomato-Cucumber Relish: In a medium bowl, combine all relish ingredients. Stir gently to mix.
Serving: Serve burgers on homemade flour tortillas with a dollop of Greek yogurt sauce and a side of tomato-cucumber relish.