Whisk together the garlic, lemon zest, lemon juice and yogurt in a small bowl to combine. Season with salt and set aside in refrigerator, covered.
In a spice or coffee grinder coarsely grind cumin seeds, peppercorns, caraway seeds, red pepper flakes, sugar and salt until only a few whole spices remain. This will be a coarse spice rub.
Clean and heat grill to 425°F, indirect heat (for a charcoal grill, bank coals on one side of grill; for a gas grill, leave one or two burners off).
In a bowl or plastic bag add cubed lamb and spice rub. Massage lamb, pressing spice blend onto the meat with your hands to coat.
Thread lamb cubes onto 8-12 skewers, leaving a small gap between each piece of meat. Drizzle with olive oil.
Grill lamb over direct heat, turning every minute or so, until browned and you see visible char marks, about 4 minutes. Move to cooler side of grill and continue to grill until lamb is cooked to desired doneness, about 4 minutes longer for medium-rare.
Allow to rest for 5 minutes on platter and serve with yogurt sauce, warm flatbread or pita and your favorite condiments (See Note 2).
Notes
1. Half a medium sized lemon should give you a tablespoon of fresh lemon juice. I also used the zest from half the lemon, cut it and then juiced it. 2. I spread the warmed pita with hummus, added pickled red onion slices and chopped cilantro for toppings with a drizzle of the lemon garlic yogurt.