Prepare the Mixture: In a large mixing bowl, combine the ground chicken, diced red onion, minced garlic, finely chopped sun-dried tomatoes, and roughly chopped spinach. Add the fresh dill, dried oregano, kosher salt, and black pepper. Using your hands or a large spoon, gently mix all ingredients until just combined. Avoid overmixing, as this can result in tough burgers.
Form the Patties: Divide the mixture into 4 equal portions and shape each into a patty about ¾-inch thick. Make a small indentation in the center of each patty with your thumb – this prevents the burgers from puffing up during cooking and helps them cook evenly.
Heat the Pan: Heat the extra virgin olive oil in a large skillet or grill pan over medium-high heat. You can also use an outdoor grill if preferred.
Cook the Burgers: Once the oil is hot and shimmering, carefully place the patties in the pan. Cook for 5-6 minutes on the first side without moving them, allowing a golden crust to form. Flip the burgers and cook for an additional 4-5 minutes, or until the internal temperature reaches 165°F (74°C) when checked with a meat thermometer.
Rest and Serve: Remove the Greek chicken burgers from heat and let them rest for 2-3 minutes before serving. This allows the juices to redistribute throughout the meat, ensuring maximum flavor and juiciness.