In a medium bowl, gently combine lamb, Greek seasoning, salt and pepper. Form into 8 patties.
Heat a large nonstick skillet over medium-high heat. Add patties and cook 3 minutes per side. Remove to a plate.
In a medium bowl, combine spinach, feta, onion, oil and vinegar; gently toss.
Place each patty on a pita with some of the spinach salad. Top with another pita and serve immediately.