In a large bowl, whisk 1 cup of the yogurt with the water. Add the lamb cubes, toss to coat and refrigerate overnight.
Light a grill. Drain the lamb and pat dry with paper towels. In a large bowl, whisk the remaining 1 cup of yogurt with the chile powder, turmeric, garlic, cayenne and 1 teaspoon of salt. Add the lamb, toss to coat and let stand for 10 to 20 minutes.
On each of 6 metal skewers, thread a piece of the lemon peel. Thread the lamb cubes onto the skewers and season with salt. In a small bowl, combine the ghee with the lemon juice.
Grill the skewers over moderately high heat, turning, until starting to char all over, about 3 minutes. Continue to grill, turning and basting with the ghee and lemon juice, until medium-rare, about 4 minutes longer. Serve the lamb on or off the skewers.