Roasted Ratatouille

globe eggplant (1 lb.), peeled and cut into 3/4 inch cubes

medium zucchini or summer squash (1 lb.), cut into 1/2 inch cubes

red onion, halved and sliced 1/4-inch thick

diced tomatoes, drained, but reserve 1/4 cup of liquid

olive oil

garlic cloves, sliced thin

fresh minced thyme or 1/4 teaspoon dried

salt

freshly ground black pepper

red wine vinegar (optional)