Place the thawed spinach in a colander and squeeze out as much excess water as you can. Transfer to a medium sized mixing bowl.
Step 2
Slice some of the red onion and set aside as burger toppings and dice the rest of it; add to the spinach along with the garlic and crumbled feta. Season with a generous amount of freshly ground black pepper. Stir in the egg and mix together with your hands until the ingredients are incorporated.
Step 3
Lay out the panko in a shallow dish and season with a bit of salt and pepper. Form 4 patties with the spinach mixture and dredge lightly in the panko. Arrange them in a single layer on a parchment lined sheet tray and chill in the refrigerator while you prepare the ranch dressing.
Step 4
To make the ranch dressing Whisk the yogurt in a small bowl along with the buttermilk, lemon zest and juice, dill, parsley, garlic and onion. Taste and season with salt and several turns of black pepper as needed. Set aside.
Step 5
Cook the burgers In a large, heavy bottomed skillet, heat a few tablespoons of avocado oil over medium high heat. When the oil is shimmering and hot place the chilled patties in the pan, laying away from you to avoid hot oil splatter. Cook for 2 to 3 minutes or until crisp and golden. Flip and do the same on the other side.
Step 6
Split the buns, dress with the ranch dressing and layer on the red onion slices, some sliced tomato and the spinach feta burger. Serve immediately.
