Heat the oil in a large skillet, add the garlic and onions and saute until the onions are transparent. Meanwhile, slice the squash and peel and cube the eggplant. Flour the pieces lightly. Add the squash, eggplant and green peppers to the skillet, cover and cook slowly about 30 minutes. Add the tomatoes and capers and simmer, uncovered, until the mixture is thick, about 10 minutes. Season with salt and pepper. Serve hot or cold.