1) Gently combine lamb, garlic, onion, mustard, salt, pepper, vinegar, oregano, and rosemary with your hands and shape into 4 oblong patties (they'll fit better in the pitas. Grill 5-6 minutes on each side and remove from heat.
2) Allow to stand 5 minutes. Place on pitas or flatbread and add onion, tomatoes, and Tzatziki. Fold like a taco and serve immediately. For easy serving andcleaning, wrap in aluminum foil.