Preparing the sauce: Rinse the mushrooms under cold running water and then soak them in the hot water for about 30 minutes. Remove and discard the mushroom stems, slice and reserve the caps, and save the soaking liquid. Carefully pour the soaking liquid into a small sauce pan, leaving behind any bits of grit or sand. Add the sliced mushrooms and the remaining ingredients. Bring to a simmer very gently for about 10 minutes
Cooking the fish: Season the fish with salt and pepper and roll them in flour. Pat them thoroughly to shake off any excess flour. In a non-stick pan, saute the fish over medium to high heat in oil until crispy on both sides (10 minutes per inch of thickness). Quickly transfer to a baking sheet covered with paper towels and pat the fish to get rid of any clinging oil. Transfer again to heated plates, pour the sauce over each fillet, and serve immediately.