Preheat the oven to 425 degrees F/220 degrees C/Gas Mark 7. Combine the eggplant, zucchini, onion, bell peppers, oil, vinegar, thyme and pepper in a large baking dish and toss to mix well. Bake, stirring occasionally, for 20 minutes, or until the vegetable are tender. Set aside. Place the pizza shells on baking sheets. Spread about 2 Tbsp. of tomato sauce on each pizza shell, then top with the roasted vegetables. Bake for 10-12 minutes, or until the pizza shells and vegetables are heated through.