Slice all veggies about the same size, in about 2″ by ¼” thick rounds. In a 9-10″ tart pan or glass pie plate, pour tomato sauce of your choice in the bottom. Dot with ricotta cheese, or, if preferred, sprinkle with parmesan cheese. Start with the outer edge. For the second row, do the same thing, but layer them in the opposite direction. For the third row inside, layer the veggies the same way as the outer row. Continue until veggie slices are used up. Drizzle with olive oil and sprinkle with salt and pepper to taste. Bake at 350ºF for about 40 minutes, or until veggies are cooked and top is slightly browned.