Steam broccoli, cauliflower, green beans, and carrots in a vegetable steamer 5 to 10 minutes, or cook covered in a microwave with a little water until crisp-tender.
Transfer to a large serving bowl. Add red pepper and mushrooms to bowl and toss to mix.
In a small bowl, combine olive oil, vinegar, scallions, and thyme with a wire whisk. Drizzle over vegetables and serve.
Recipe provided by Low Cholesterol Olive Oil Cookbook