Place cashews in baking dish and bake at 350F for 10 to 15 minutes, or until they give off a fragrant odor and are lightly roasted. Stir the cashews occasionally while they bake to make sure that they brown evenly. Set aside.
While the nuts are roasting, combine the zucchini, red pepper, and mushrooms in a large bowl. Add 1 tablespoon olive oil and 1 tablespoon tamari. Mix well. Place a rack with small holes over the bottom rack of your grill. Transfer the vegetables to the rack and cook over low heat, stirring often, until they are tender but still crisp (10 minutes or less). Put a large kettle of water on to boil while the vegetables are cooking.
Place the roasted vegetables in a salad bowl and chill.
Cook the pasta in boiling water according to the directions on the package. Drain the pasta and rinse briefly under cool water.
Add the cooked pasta to the vegetables. Add the parsley and scallions.
In a small bowl, combine the ingredients for the dressing. Pour this dressing over the vegetables and pasta. Mix well and refrigerate about 2 hours.
Add the cashews and mix again just before serving.