Cook the noodles while preparing the salmon and sauce.
Stir together the soy sauce, sake, mirin, and broth. Set aside.
Put oil in a pan over medium heat. Put the salmon filets in and turn to coat. Sprinkle with garlic and ginger. Cook for about 5 minutes, until the seasonings start to brown and the outside starts to turn pale pink, then turn over.
Pour the sauce over the salmon. Cook over medium heat, covered, for about 5 more minutes. Sprinkle fresh pepper on top.
When salmon is opaque all the way through, remove from heat. Add cooked noodles to the skillet and stir for a minute or two. Pour noodles onto plates and place salmon on top. Garnish with fresh scallions.