Spread the walnuts on a baking sheet and roast them for 5 minutes, just until they turn slightly more brown (this can also be done in a small skillet on top of the stove. Stir them constantly so they don't burn).
Set a large saute pan containing the oil over low heat for less than a minute. Drop in the garlic and the shallots. Add the soy sauce, wine, and mushrooms and simmer covered until the mushrooms are tender, about 10 minutes. Use a slotted spoon to shake the mushrooms so the cooking liquid falls back into the pan (reserve the liquid), then place the drained mushrooms, cavity-side-up, in a baking dish.
Bring the stock or water to a boil in a separate pot, pour in the couscous, reduce the heat, and simmer covered for two minutes. Remove from heat and let it stand, covered, for 10 minutes, until all the liquid is absorbed. Dump the couscous into the skillet with the reserved mushroom liquid and cook over low heat until all the liquid is absorbed.
Lightly season the mushroom caps with salt and pepper. Mix the remaining ingredients, including the nuts, into the cooked couscous. Using a tablespoon, pile a small mound of filling inside the cap of each mushroom. Bake for 10 minutes or until the stuffing is lightly browned on top.