Preheat oven to 400 degrees F. Line a 3-quart rectangular baking dish with foil and coat with cooking spray; set aside.
Halve the squash lengthwise. Remove seeds with a spoon, leaving a shell about 1/4 inch thick. Place squash halves, cut sides down, in prepared baking dish. Bake, uncovered, for 10 minutes. Turn squash halves cut sides up.
Meanwhile, for filling, in a medium bowl, stir together cream cheese, carrot, blue cheese, green onions, 1/4 cup of the bread crumbs, the sour cream, and pepper. (the mixture will be stiff.)
Spoon filling evenly into squash halves. Top with walnuts and remaining crumbs. Bake, uncovered, about 10 minutes or until squash is tender and filling is heated through.
To make ahead: Prepare as directed through Step 3. Cover and chill for up to 24 hours. Bake as directed in Step 4, except bake about 15 minutes.
1 vegetables, 1/2 fat, 1/2 high-fat protein