Heat oils in a skillet or wok. Add ginger and stir fry a few seconds or until you can smell it, add garlic and mushrooms and stir fry a few moments. Add sugar, mirin and fish. Cover and simmer over low heat until fish is just cooked through, about 5 minutes.
Remove from heat and add dissolved miso. Mix well, season to taste with salt and crushed red pepper; stir in scallions and cilantro; serve over brown rice.