In large Dutch oven heat 2 tablespoons salad oil. Cook carrots and 1/4 teaspoon salt until carrots are tender-crisp (about 3-5 minutes), stirring often. Remove carrots to a large bowl.
In 2-3 more tablespoons salad oil stir mushrooms and 1/4 teaspoon salt. Cook 3-5 minutes. Remove to large bowl.
In 1 tablespoon oil cook tomatoes until heated through (about 1 minute). Remove to large bowl. In 2 more tablespoons oil cook broccoli, cauliflower and onion. Add water, 1/2 teaspoon salt and cook 5-10 minutes until tender-crisp, stirring occasionally.
Remove Dutch oven from heat - return all vegetables to Dutch oven. Add soy sauce; mix well. Heat 1-2 minutes until hot. Spoon vegetables on a layer platter. Serve hot or refrigerate and serve cold later.
