Place eggplant, zucchini, onion and mushrooms in a 2 quart casserole dish. In a small bowl combine the tomato paste with the water, and stir in garlic, basil, salt and pepper. Pour over the vegetables and mix well.
Bake in preheated oven for 45 minutes, or until eggplant is tender, stirring occasionally. Add water as necessary if vegetables begin to stick; however, vegetables should be fairly dry, with slightly browned edges.
