Preheat oven to 400°.
Place bread cubes onto a rimmed baking sheet. Bake at 400° for about 10 minutes or until golden brown, stirring once. Remove from oven and let cool at least 5 minutes.
Heat butter and olive oil in a medium skillet over medium-high heat. Add onion, carrot, celery and sage to pan; cook 4-5 minutes or until tender, stirring occasionally. Remove from heat. Combine stock and eggs in a medium bowl, stirring with a whisk. Add bread, sautéed vegetables, parsley, salt, and pepper; toss to coat and let stand 5 minutes or until liquid is absorbed.
Cut top quarter off of each squash. With a spoon, scrape out and discard seeds and pith; leaving a ¾-inch edge inside squash. Cut a thin slice from the bottom of each squash so they sit flat and level. Divide bread mixture evenly among squash. Arrange on a baking sheet lined with parchment paper. Bake at 400° for 35 minutes or until tender when pierced with a sharp knife.
Note: You can also make a batch ahead of time and bake just before serving.
Recipe adapted from: www.cookinglight.com