Place squash in a large saucepan. Cover with water.
Bring to a boil, cover with the lid and cook for about 7 minutes or until crisp-tender. Then drain the water.
When cool enough to handle, cut squash in half lengthwise. Scoop out and reserve the pulp, leaving a ⅜-inch shell. Invert shells on paper towel.
In a small bowl, combine the egg substitute salt, onion, and pepper. Stir in the toasted bread crumbs cubes and squash pulp. Spoon into the squash shells.
Place in a 8-inch , square baking dish coated with cooking spray.
Cover and bake at 375° for about 20 minutes. Uncover, and bake until lightly browned about 5-to 10 minutes longer.