In small, heavy saucepan bring soy sauce, mirin and vinegar to boil. Reduce heat and simmer for 5 minutes or until it gets syrupy.
Toss beef cubes and green onions with the oil. Thread beef and onions onto skewers, use 3 onion pieces in between each beef cube(1,3,1,3,etc).
Heat grill,lightly oil grill . Grill skewers for 1 minutes on each side, brushing with the glaze. Transfer to your serving platter and brush lightly with glaze again...great served with basmati or jasmine rice, maybe corn on the cob or grilled squash?