If using fresh green beans, precook, covered, in a medium saucepan in a small amount of boiling water for 10 minutes. Drain; set aside.
Place margarine or butter in a wok or large skillet. (Add more margarine as necessary during cooking.) Preheat over medium-high heat until margarine melts. Stir-fry green beans in margarine for 3 minutes.
Add mushrooms; stir-fry for 1 to 2 minutes more or until vegetables are crisp-tender. Add water, basil, sugar, salt, and pepper. Cover and cook about 3 minutes or until just crisp-tender. Add tomatoes; toss to combine. Serve immediately. Garnish with fresh basil, if desired. Sprinkle with Parmesan cheese, if desired. Makes 4 servings.