Make the special sauce: Add the light mayonnaise, sweet pickle relish, ketchup, onion powder, garlic powder, salt, and apple cider vinegar to a bowl. Thoroughly mix, then set aside.
Prep the toppings: Dice the onion, slice the lettuce, and finely dice the tomato.
Season the meat: Season the ground turkey with salt, pepper, onion powder, and garlic powder. Then, use your hands to roll the ground turkey into eight, 2-ounce balls.
Cook the smash burgers: Heat a skillet over medium-high heat and lightly spray with oil. Place a ground turkey ball in the pan, cover with a tortilla, and press down with a spatula, meat press, or heat-resistant bowl until thin. The meat needs to be a thin layer so it cooks. Once smashed down, let it cook for 3 minutes.
Flip and cook: Flip, top with cheese, cover, and cook for 2-3 more minutes, or until fully cooked. Then, repeat this process for the rest of the smash burger tacos.
Serve: To serve, top with lettuce, tomatoes, onions, pickles, and the homemade special sauce. Enjoy these smash burger tacos warm.