Add another drizzle of olive oil to the skillet, add the onions and garlic to the pan. Cook the onions, stirring occasionally, until they are wilted and lightly caramelized, about 5 to 7 minutes. Add the eggplant and thyme to the pan and continue to cook, stirring occasionally, until the eggplant is partially cooked, about 5 minutes. Add the red peppers, zucchini, and squash and continue to cook for an additional 5 minutes. Add the canned tomatoes balsamic vinegar, basil, oregano, salt and pepper, to taste, and cook for another 5 minutes. Serve warm over the creamy, cheesy polenta.