Start by preheating your outdoor grill to medium-high heat (about 375°F to 400°F). Clean the grates thoroughly with a grill brush and lightly oil them to prevent the lean turkey meat from sticking.
In a large mixing bowl, combine the ground turkey, crumbled feta, chopped spinach, beaten egg, minced garlic, Worcestershire sauce, and all the spices. Use your hands or a fork to mix everything together until just combined. Be careful not to overwork the meat, as this can make the burgers tough.
Divide the mixture into four equal portions. Shape each portion into a patty about 1 inch thick. Use your thumb to make a slight indentation in the center of each patty; this prevents the burger from “puffing up” in the middle while cooking.
Place the patties on the hot grill. Close the lid and cook for 5 to 6 minutes per side. Turkey burgers must be cooked until they reach an internal temperature of 165°F (74°C) to be safe and delicious.
Once the burgers reach the proper temperature, remove them from the grill and place them on a clean plate. Let the meat rest for 3 to 5 minutes. This allows the juices to redistribute throughout the patty, ensuring every bite is moist.