We like this recipe because we use fresh peppers, onions, and zucchini from our garden. I can up with this recipe because I needed a quick recipe for unexpected company and had left over marinara sauce in the refrigerator and breakfast sausage in the freezer. I usually make my recipe with ziti, however, penne pasta is basically the same thing. I make this recipe in the summer when I have lots of "fresh" zucchini from my garden. I always pick fresh, baby zucchini for this recipe, therefore, it isn't necessary to peel the zucchini or cook it, because it is very tender. When it is sliced thin, it cooks perfectly in the casserole and does not require prior cooking. I serve this with fresh garden salad and crusty bread or rolls.