Heat 1 tbsp olive oil in a skillet on medium heat. Add the sliced onions, sprinkle with salt and cook for 12 to 15 minutes until they have softened and begun to caramelize. Add in the spinach and cook for 2to 3 minutes until it has begun to wilt and then remove from the heat.
In a bowl combine all of the ingredients including the onion and spinach and mix with your hands to really combine everything together.
Form the mixture into 8 to 10 patties
Cook the patties in the skillet in 1 tbsp olive oil for approximately 5 minutes per side until golden brown on and outside and cooked through in the center.