Preheat oven to 350°. Reheat Potato Cakes according to recipe instructions on page 105.
Cut squash lengthwise into 4 slices each. Sprinkle squash and mushrooms with pepper, and coat with cooking spray. Place on grill rack coated with cooking spray; grill 3 minutes on each side or until tender. Remove from heat. Chop squash; set aside.
Pour pasta sauce into a 2-cup glass measure. Cover and microwave at HIGH 2 minutes or until thoroughly heated, stirring after 1 minute.
Place mushroom caps on plates; top each with a potato cake. Spoon squash over potato cakes. Top each with pasta sauce, and sprinkle with cheese.