Heat oil in a large frying pan over high heat. Add yellow onion to pan, fry until onion softens and looks translucent. Add mushrooms, ginger and ground pork. Lower heat to medium. Add sake, mirin, soy sauce and chicken broth. As mixture cooks, break up the pork as much as possible. Stir-fry to reduce sauce and brown meat. Add green onions and cook for additional minute. Stir well and serve over rice (brown or white) or noodles.