1 cup soy sauce
1/2 cup mirin (sweet Japanese rice wine) or sweet sherry
1/2 cup (packed) dark brown sugar
1/4 cup unseasoned rice vinegar
1/4 cup oriental sesame oil
1/4 cup minced garlic (about 15 cloves)
2 large green onions, chopped
5 pounds Korean-style short ribs (beef chuck flank, cut 1/3 to 1/2 inch thick across bones, about 20 pieces)

Combine the first 7 ingredients in medium bowl; whisk to blend well.  Pour into heavy jumbo resealable plastic bag.  Add ribs; seal bag.  Turn bag over several times to coat ribsribs evenly.  Refrigerate overnight, turning bag occasionally.

Prepare BBQ (medium-high heat).  Drain ribs, discard marinade.  Working in batches, grill ribs until browned and cooked to medium-rare, about 3 minutes per side.  Mound ribs on platter; surround with chopped spinach and serve.