In a large mixing bowl, add the ground turkey, spinach, feta, onion, garlic, Greek seasoning, salt, and pepper. Mix until combined.
Chill in the refrigerator for 30 – 60 minutes.
Divide the mixture into 12 patties.
Using a large skillet or cast-iron pan, add the avocado or olive oil over medium-high heat. Working in batches, cook four patties at a time in prepared skillet. Cook burgers for 4 minutes per side or until cooked through.
If they seem to be cooking too fast on the outside, reduce the heat to medium.