Preheat grill or position an oven rack 4-5 inches from the broiler element and heat the broiler to high.
In a small bowl, combine the lemon juice, sour cream, garlic, and a pinch of salt. Slowly whisk in ¼ cup olive oil.
In a medium bowl, combine the lamb with the 1 tablespoon olive oil, ½ teaspoon salt, and ¼ teaspoon pepper. Toss to coat evenly. Thread the lamb onto four small (8-inch) bamboo or metal skewers.
Put the skewers on the grill or on a broiler pan and broil the lamb, flipping once, until browned on the outside but still pink inside. These lamb kebabs are best served medium rare, 145 degrees internal temperature., 2 to 4 minutes per side.
Transfer the skewers to a small, shallow baking dish. Whisk the vinaigrette to recombine and pour 3 tablespoon over the skewers, turning to coat.
In a medium bowl, toss the arugula and onion with enough of the remaining vinaigrette to lightly coat (you may not need it all). Season with salt and pepper to taste.
Pile the greens on two plates, top each salad with two lamb skewers, sprinkle with the cheese, and serve immediately.