How to Make It
In a medium bowl, combine the white vinegar with the Dijon mustard and agave nectar. Stir in the onion slices and season with salt and white pepper.
Light a grill or preheat a grill pan and oil the grates. In a large bowl, toss the lamb with the 1 tablespoon of peanut oil and season generously with salt and black pepper. Thread the lamb pieces onto 8 skewers. Grill the lamb over moderate heat, turning occasionally, until it is charred in spots, 6 to 7 minutes for medium meat. Transfer the lamb skewers to a platter and serve with the mustard onions.