In a medium bowl, combine the ground chicken, red onion, garlic, sun-dried tomatoes, spinach, dill, oregano, salt, and pepper. Use your hands to mix everything together until well combined.
Divide the mixture evenly into four portions and shape each portion into large patties about ¾ inch thick.
In a large skillet over medium heat, add olive oil and allow it to heat up before placing the patties in the pan. Cook them for about 5 minutes on each side, or until they are golden brown and fully cooked through.
Once cooked, remove the patties from heat and let them rest briefly before assembling your burgers. Layer your favorite toppings such as tzatziki sauce, crumbled feta cheese, sliced onions, tomatoes, and avocados on top of butter lettuce or inside pita bread.