Combine first 7 ingredients in a saucepan; bring to a boil. Cool.
Cook Brussels sprouts according to package directions; drain.
Cut bell peppers into thin strips. Slice onion, zucchini, and yellow squash; separate onion into rings. Cut broccoli into flowerets. Drain olives and artichoke hearts. Place vinegar mixture and vegetables in a large zip-top plastic bag. Seal and chill 8 hours, turning occasionally.
Add mushrooms and tomatoes, and toss gently. Serve immediately.