With a sharp knife cut squash crosswise into 2-inch-thick slices. Working with 1 slice at a time, cut side down, cut away peel and seeds and cut squash into 1-inch cubes (about 9 cups).
In a large bowl stir together squash, bell pepper, oil, garlic, herbs, black pepper, and salt to taste. Transfer mixture to a 2- to 2 1/2-quart gratin dish or other shallow baking dish and sprinkle evenly with Parmesan.
Bake casserole in middle of oven until squash is tender and top is golden, about 1 hour.
