For the marinade, pulse the onion in a food processor until pureed. Add the remaining ingredients and pulse just until combined. Pour the marinade over the lamb cubes in a shallow nonaluminum container and toss the meat to coat. Cover and refrigerate overnight.
Heat the grill or broiler. Let the lamb warm to room temperature. Thread the cubes onto 6 skewers and lightly sprinkle with salt. Grill or broil 3 to 4 minutes each side until medium-rare. Remove the lamb from the skewers and serve on top of a bed of rice pilaf, accompanied by a salad of diced cucumbers, yogurt, and mint.