If using wooden skewers, soak in water 30 minutes. In a small bowl combine first six ingredients (through cayenne pepper).
Thinly slice meat diagonally across the grain into long strips. Thread meat accordion-style onto skewers, leaving 1/4 inch between pieces. Lightly brush with oil; sprinkle with half of the spice mixture.
Grill meat skewers, uncovered, over medium heat 5 to 6 minutes or until meat is slightly pink in center, turning once. Grill lemons, cut sides down, the last 2 to 3 minutes or until lightly charred.
To serve, sprinkle meat with remaining spice mixture, red onion, cheese, mint, and, if desired, pine nuts and/or Greek yogurt. Squeeze juice from lemons over meat. Serve with pita bread.