Sliced zucchini and shredded carrots team up to make this tasty zucchini stuffing casserole recipe. Some of the stuffing cubes add flavor and body to the filling, while some make up the buttery topping. This casserole is an excellent way to use prolific fresh zucchini, and the stuffing mix makes it a filling side dish. Go ahead and use yellow summer squash if that's what you have. Or use a combination of zucchini and summer squash. For a burst of color, add a few tablespoons of diced red bell pepper, roasted red bell pepper, or pimientos. This dish can easily be transformed into a main dish casserole with about 2 cups of diced chicken or turkey. If the stuffing crumbs are bland in flavor, amp them up with a teaspoon or two of poultry seasoning, herbes de provence, or an italian herb blend. Feel free to add extra onion if you'd like. If you're making this a vegetarian dish, check the labels on the stuffing cubes to make sure there isn't any chicken listed in the ingredients. Or make a batch of seasoned stuffing cubes from scratch (below).