Prepare the vegetables: Cut the eggplant, zucchini and potatoes in bite sized chunks (do not peel the zucchini or the eggplant). Remove the stems and seeds from the peppers and slice them into strips. Peel and slice the onions. Dice the tomatoes.
Saute the vegetables except the tomatoes in the olive oil in small batches. Saute each batch for 2 or 3 minutes, then remove from the pan, trying to drain some of the oil so that enough oil is left for the next batch. When you're done, most (if not all) of the oil should be gone from the pan.
Place the sauteed vegetables in a baking dish and toss them briefly so that you won't get only one kind of vegetable in one place.
Add the tomatoes into the pan and saute for a couple of minutes. Crush the garlic and add to the tomatoes. Add the sugar, salt and pepper to taste and simmer for another minute.
Pour the tomato sauce on top of the vegetables.
Bake at 350F degree until the vegetables are tender.
Serve with plenty of fresh bread and, if you like, some feta cheese on the side.