Combine lamb, garlic, cumin, coriander, pepper, salt, mint and parsley. Shape mixture into 4 patties. Grill patties over med-high heat, for 6 minutes per side, or until internal temperature reaches the desired temperature. Medium-Rare 145 F; Medium 160 F; Well-Done 170 F
To make sauce: Combine yogurt, diced cucumber, 1⁄4 c pistachios, cilantro, salt, and red pepper.
Cover and chill up to 2 days. Spread the desired amount of cucumber sauce over pitas. Top with lamb patty. Garnish with sliced cucumber and remaining 1⁄4 c chopped pistachios.