In a small saucepan, whisk together the vinegar, oil, onion, sugar, salt, basil, oregano and garlic powder. Bring mixture to a boil; cover, reduce heat and simmer 12 minutes.
In a large bowl, add the artichoke hearts, broccoli, cauliflower, carrot and mushrooms. Pour the vinegar mixture over all and toss to coat. Cover and chill at least 3 hours. Serve using a slotted spoon.
