In a large heavy saucepan, heat the olive oil over medium-high heat. Add the carrots, onions, 1 tablespoon salt and 1 teaspoon pepper. Cook, stirring frequently, until the onion begins to brown, about 6 minutes.
Add the parsley, thyme, garlic, tomatoes and zucchini, and cook for 3 minutes. Add the chicken broth and bring to a boil. Slowly stir in the polenta and cook until the soup thickens and the vegetables are tender, about 8 minutes.
Stir in the butter and season with salt and pepper.