Place squash in a pot fitted with a steamer basket over boiling water, and steam 10 minutes, or until tender.
Preheat oven to 350 degrees F (175 degrees C). Lightly grease a medium baking dish.
In a bowl, mix the squash, cornbread, margarine, sage, cream of mushroom soup, egg, onion, sugar, salt and pepper, and milk. Transfer to the prepared baking dish.
Bake 30 minutes in the preheated oven, or until lightly browned.
