Preheat oven to 425 F.
Combine turkey, spices (except sumac), and olive oil in a bowl and mix (easiest to do with your hands).
Form a log and divide it in half. Divide each half in half again to make 4 equal portions, or divide them in three parts to make 6 equal portions for a lighter portion size. At this point you can freeze the balls for later use.
For each burger, press flat to form a patty. Coat each side with 1/2 teaspoon sumac. Set on silicone baking mat.
Bake in oven for 20 minutes. Flip burgers and bake an additional 5 minutes. If you want to toast the hamburger buns, place in oven last 5 minutes if frozen or last 2 minutes if not frozen.
Peel and grate half a cucumber, omitting the seeds. Squeeze the water out of the grated cucumber.
Mix grated cucumber with yoghurt, salt, mint, and sumac or lemon juice.
Top bun with tzatziki and burger, add lettuce to burger, enjoy :)
