Preheat oven to 450°F Line a rimmed baking sheet with foil.
Place onion, pepper, mushroom, and zucchini on prepared baking sheet. Spray vegetables lightly with cooking spray. Roast vegetables, turning once, for 30 to 35 minutes, or until tender.
Meanwhile, in a small bowl, combine pesto and sour cream.
Once vegetables are roasted, cut into pieces that fit the shape of the bread. Toss with oil, vinegar, and garlic.
Spread pesto mixture over bread; top with vegetable mixture and Brie. Cut in half.