Dissolve the miso in the water. Dissolve the cornstarch in a small amount of hot water and add to the miso, along with the soy sauce and 5-spice mix. Set aside.
Heat the wok, then add the oil; heat for a minute and swirl around to coat the wok. Add the garlic and ginger, stir around until the garlic starts to brown. Add the mushrooms, toss for about 3 minutes until they start to soften. Add the carrots, stir for about 2 minutes; then the broccoli, another minute; then the water chestnuts, another minute; then the tofu. Add a splash of sake, stir for another minute or two as the steam melds everything, then pour on the sauce. Stir until it thickens (about 3 minutes), then serve with rice or noodles.
The portabellos have a chewey, firm body and a rather strong flavor, very nice! I think next I'll try some kind of dish mixing whole caps with eggplant...I'll let you know in a week or so!
as always, "eat! eat!"