Step 1

Coat a large saute pan with olive oil, toss in the diced onions and season with salt and crushed red pepper. Bring the pan to medium-high heat and cook the onions for 3 to 4 minutes. Add the garlic and cook for 2 to 4 more minutes. Turn the heat off and let cool.

Step 2

In a large bowl, combine the lamb, the cooled onion mixture, the oregano, dill, mint, lemon zest and 1/2 to 3/4 cup water. Sprinkle with salt and combine well. Make a little "tester patty." Cook it and taste for seasoning.

Step 3

Preheat the grill.

Step 4

Form the lamb mixture into 4 equal patties and sprinkle with salt. Grill the burgers to your desired doneness, 4 to 5 minutes per side for medium-rare. Remove the burgers from the grill and let rest for 3 to 4 minutes.

Step 5

Cut the pitas in half. Schmear each half generously with the Feta Tzatziki Spread. Top one half with a burger, then tomatoes, sliced onions and spinach. Place the other pita half on top.

Step 6

Combine the yogurt, feta, vinegar, garlic, mint, dill and cucumbers. Season with salt. Let sit for at least 1 hour at room temperature before serving.