Make the tzatziki sauce first so the flavors have a chance to meld. If you drain the yogurt first, your sauce will be super thick and delicious. Combine all sauce ingredients, stir well and refrigerate.
You can either buy drained yogurt (known as Greek, Hungarian or Bulgarian yogurt, and maybe you can find it under other names, it's all the same, and it's very thick) or drain your own. I drain mine by putting it into a coffee filter over a deep container and popping it into the refrigerator for about 24 hours. All of the liquid will drain out and the yogurt will be super thick. I start with 16 ounces and it drains down to about 8 or 10 ounces, which is perfect for the 4 patties the recipe makes. Discard the liquid.
To paste the garlic, mince it finely then add a bit of salt to the pile. Lay your blade flat on top of the pile and, with the heel of your hand, apply pressure and push down and away. The salt will act as an abrasive and break the bits of garlic down. After a couple of minutes of this, the garlic will be a paste. Once the garlic is a paste, it will go all through the yogurt smoothly without leaving chunks.
Now, to the patties. In a large mixing bowl, combine ground chicken, onion, and garlic. Squeeze all the water out of the spinach and separate it as you add it to the bowl. Crumble the feta cheese into the bowl. Add the breadcrumbs, egg, steak seasoning, salt and 1 tbsp of olive oil. Mix it all together so that all the ingredients are evenly distributed, but don't overwork it.
Form the mixture into 4 patties and drizzle each with the remaining olive oil, turning to coat both sides.
Brown the patties in a medium hot skillet, about 6 minutes on the first side, and about 4 minutes on the 2nd side. You're looking for a nice brown color on each side. To get the best color, once you put them in the skillet, don't move them until you're ready to flip. Your nose will tell you when they're ready.
If you use a non-stick skillet, the olive oil you've drizzled over the patties will be sufficient and there will be no need to add more oil to the skillet.
Warning! Your house will smell phenomenal!
Serve the patties with a Greek salad, some warm pita bread, and the tzatziki on the side.