Combine the broth or water and bouillon cube with the wild in a large saucepan and bring to a slow boil. Stir in the brown rice. Cover and simmer gently until the water is absorbed, about 35 minutes. Let the rice cool to room temperature.
Heat the olive oil in a wide skillet or steep-sided stir-fry pan. Add the shallot or onion and sauté over medium-low heat until translucent.
Add the garlic, celery, and bell pepper, and continue to sauté until the mixture is beginning to turn golden-brown.
Add the mushrooms to the skillet and continue to cook until they're wilted and beginning to give off liquid.
Once the wild and brown rice mixture is done, add to the skillet along with the parsley and walnuts. Stir together and season with salt and pepper.
Continue to cook for 5 minutes longer, then remove from the heat. Serve hot or warm.