Chop eggplant to make one cup. Cut the remaining eggplant in half lengthwise, and slice thinly.
Heat 1 tablespoon of olive oil in a medium skillet. Add garlic and onions and cook until the onion is tender.
Stir in chopped eggplant, chopped tomatoes, dried oregano, salt, pepper and sugar. Cook uncovered over medium-low heat, about 15 minutes. Liquid should be evaporated and mixture should be of spreading consistency. Stir occasionally during cooking, and then remove from heat.
On a lightly greased baking sheet, place the bread shell.
Spread the warm tomato mixture over the bread shell, and arrange the eggplant and tomato slices around the edge. In the center, arrange the zucchini and yellow squash.
Brush the vegetables with the remaining olive oil, and sprinkle with feta cheese and olives, and top with mozzarella cheese.
Bake for 12 to 15 minutes in a 400° oven. Vegetables will be warm, and cheese melted.