Source: Spiral Path Farm (http://www.spiralpathfarm.com/acorn_squash.html)
3 onions, chopped
2 Tbsp oil
1 cup diced celery
1 bunch spinach, coarsely chopped
1/2-1 C. whole wheat bread crumbs
1/2 tsp salt
Preheat oven to 350 degrees. Halve squash; remove seeds. Place face-down in greased baking dish; bake until fork-tender, 25-45 minutes. Meanwhile, saute onions in oil until soft. Add celery; cover and simmer on medium heat until just tender. Stir in spinach; cook until wilted. (Raise eat to cook off any extra moisture). Stuff squash with vegetable mixture. Sprinkle with bread crumbs and salt.
Bake 10-15 minutes.