Add baby spinach leaves into a bowl of a food processor and process until finely chopped.
1-3 cups loosely packed baby spinach
In a large bowl, gently mix everything together, along with the spinach. Use your hands to mix until just combined. You don't want to over-mix otherwise the burgers will be tough.
1 pound ground turkey, 1 teaspoon garlic powder, 1 teaspoon Kosher salt, 1/2 teaspoon ground black pepper, 1/4 teaspoon crushed red pepper flakes, 2/3 cup feta crumbles
Form four relatively equal-sized patties and let rest on a plate while you heat up the skillet or grill.
If making this indoors on the stovetop, use a cast iron skillet or nonstick skillet and place it over medium-high heat with a little bit of cooking oil. Once heated up, place the patties, two at a time, into the skillet and cook until both sides are brown and it is cooked through (internal temperature of 160 °F (71 °C)).
If making this on the outdoor grill, turn your grill on high and cook patties on both sides until cooked through (internal temperature of 160 °F (71 °C)) and nicely browned on the outside.
Serve with your favorite buns and toppings (hummus, red onions, tapenade, etc.)