In a large skillet, heat 2 tablespoons oil over medium-high heat for 2 minutes until sizzling hot. Add onions and garlic and sauté until tender and nicely browned, about 2-3 minutes. Set aside on a plate for 5 minutes to cool down slightly.

In a large mixing bowl, add ground turkey, sautéed onion and garlic, breadcrumbs, dill, lemon juice, cumin, salt, and pepper. Stir well with a spatula to combine everything together (or use your hands to press the ingredients together to evenly combine).

Shape the ground turkey mixture into a firm ball. This helps the mixture bind together to yield firm patties. Cover the bowl with plastic cling wrap and refrigerate for at least 30 minutes, up to overnight.

Divide the turkey mixture into 4 equal parts and use your hands to roll them into balls. Then, shape them into patties by flattening them in the palm of your hand until they are about ½-inch thick.

Heat the remaining 1 tablespoon olive oil in a cast-iron skillet over medium-high heat until sizzling hot, about 2 minutes. Place patties on the skillet and cook for 3-5 minutes until nicely seared and starting to brown up the sides. Flip the patties over and cook for another 3-5 minutes, until the internal temperature for the patties reaches 165 F as read on a meat thermometer.

Slice the hamburger buns in half and toast them on the grill, if desired.

On each hamburger bun, add a piece of lettuce and a turkey patty. Drizzle 1 to 2 tablespoons of tzatziki sauce on top, and top the patty with a slice of tomato. Place the top half of the bun on top to assemble the burger.

Serve with a side of crispy french fries or a side salad such as coleslaw or macaroni salad.