Make yogurt sauce: Mince and mash the garlic with the salt. Drain yogurt in a sieve lined with a dampened paper towel set over a bowl 30 minutes. Transfer to a small bowl and combine with the garlic and mint.

Prepare grill and oil rack. Set grill 5-6 inches from coals. In a bowl gently combine the lamb,feta and olives. Form into 6 patties about 3 cm thick. Season to taste with salt and pepper. Grill for about 7 minutes per side for medium-rare. Split pitas form a pocket.Transfer burgers to pita pockets and top with tomatoes, bell peppers and onion. Serve burgers with yogurt sauce.