Cut squash in half lengthwise, scoop out seeds.
Add water to your steamer and bring to a low boil. Add the squash, cut side down, to the steamer tray, and steam for 15 minutes or until tender, drain squash well. Work in batches to get all the halves steamed. (15 minutes for small to medium squash, 20 minutes for large.)
Place squash halves cut side up in a 9x13 inch baking pan.
While the squash is steaming, cook the sausage in a pan, breaking up the sausage with a spatula. Cook until no more pink is visible and it is cooked through. Drain off excess fat. (I went overboard and cooked up 2 lb of sausage thought I was using 2 large squash but turned out to be 1 large and 1 small, the excess was saved for another use.)
Preheat your oven to 200° C (400° F).
Add the onion and breadcrumbs, and stir together. Add a little milk or water if the sausage seems too dry.
Spoon sausage mixture into the squash, pressing down lightly.
Bake for 10-15 minutes or until lightly browned and squash is heated through.
Serve and enjoy.