1 1/2poundstop sirloin steaktrimmed and cubed into 1 1/2 inch pieces
1 1/2poundsshiitake mushroomsstemmed, halved if large
1large red onionquartered through root end, each quarter cut into 1 inch pieces
2tablespoonsminced fresh cilantro
1/2head napa cabbagecored and shredded (5 1/2 cups)
Salt and pepper
Whisk hoisin, soy sauce, 2 tablespoons oil, ginger, garlic, and pepper flakes together in medium bowl; set aside 2 tablespoons hoisin mixture in large bowl. Add beef to remaining hoisin mixture in bowl and toss to coat. Thread beef, mushrooms, and onion evenly onto eight 12-inch metal skewers, then brush each skewer with leftover hoisin mixture in bowl.
Add vinegar and cilantro to bowl with reserved hoisin mixture. Whisk in remaining 1 tablespoon oil until incorporated. Add cabbage, toss to coat, and season with salt and pepper to taste.
Grill kebabs, covered, over hot fire, turning as needed, until lightly charred on all sides and meat registers 130 to 135 degrees F (for medium), about 10 minutes. Transfer kebabs to platter, tent with aluminum foil, and let rest for 5 minutes before serving with slaw.