Prepare lamb: Sprinkle lamb with salt. In a bowl, whisk together vinegar, oil, shichimi togarashi, mirin, fish sauce, soy sauce, garlic, and ginger. Add lamb and toss to coat. Chill, covered, at least 4 hours or overnight.
About 30 minutes before cooking, soak six 10-in. bamboo skewers in water and let meat stand at room temperature. Heat a grill to medium-high (350° to 450°), or set a grill pan on the stove over medium-high heat.
Remove lamb from marinade (save marinade) and thread onto skewers. Make sauce: Bring marinade to a boil in a small frying pan over medium heat, stirring occasionally; set aside.
Grill lamb (covered if on an outdoor grill), turning occasionally, 7 to 8 minutes total for medium-rare.
Serve lamb with rice, sauce, and grilled vegetables, if you like.
* If boned lamb shoulder isn’t available, buy 3 lbs. bone-in shoulder chops. The Japanese seasoning blend called shichimi togarashi typically contains a mix of chile flakes, citrus zest, seaweed, sesame seeds, and other seasonings. Find it in the international aisle at well-stocked grocery stores, at Asian markets, and at oaktownspiceshop.com.