Over medium-low heat, add the oil to a large skillet with the onion, garlic, and bay leaf, stirring occasionally, until the onion has softened. Add the eggplant and cook, stirring occasionally, for 8 minutes or until the eggplant has softened. Stir in the zucchini, red bell pepper, tomatoes, and 1 teaspoon salt, and cook over medium heat, stirring occasionally, for 5 to 7 minutes or until the vegetables are tender. Stir in the basil and a few grinds of pepper to taste.
Cook ziti according to the label directions. Drain the ziti, then toss with ricotta cheese, eggs, olive oil, Parmesan, and 1 teaspoon salt. Spoon half the ziti into a lightly greased 4-quart casserole. Top with the ratatouille and then the remaining ziti. Sprinkle with Cheddar. Cover and bake in a preheated 350º F oven for 20 minutes. Uncover and cook 10 minutes more.