Preheat oven to 400 degrees F (200 degrees C). Bring a pot of salted water to a boil.
Thinly slice the Scallion (2). Finely chop the Garlic (2 clove) and slice the Red Onion (1) into 1/2 inch slices. Cut the Sweet Potato (1) in half lengthwise and then into wedges.
Toss the sweet potato wedges with Olive Oil (1 tablespoon), Salt (to taste) and Ground Black Pepper (to taste). Spread out on a foil-lined baking sheet with the sliced red onion. Roast for 20 min, flip after 10 min.
Once the water is boiling, add the Fresh Spinach (5 ounce) and cook for about 30 seconds until slightly wilted. Drain and squeeze out all the excess moisture. Then, coarsely chop it.
In a bowl, combine Ground Turkey (12 ounce) with sliced scallions, Feta Cheese (2 ounce) and chopped spinach. Season with a large pinch of salt and a pinch of pepper. Mix with your hands.
Heat Olive Oil (1 tablespoon) in a pan over medium-high heat. Form the ground turkey mixture into two patties and sear for about 3 minutes on each side, or until golden brown.
Transfer the burgers to the oven and cook for 8-10 min.
Combine the Mayonnaise (1 tablespoon) with the chopped garlic and spread onto the Hamburger Bun (2). Toast for about 3 minutes, or until warm and toasted.
Place the cooked turkey burgers on the hamburger buns with a slice of roasted red onion on top. Serve with sweet potato wedges on the side.