Place oven rack in center position of oven. Preheat to 425°F. Line a baking sheet with foil (lightly misted with cooking spray) OR parchment paper.
Wash and dry zucchini, and cut into 1/4-inch thick slices. Arrange zucchini rounds on prepared pan, with little to no space between them. If desired, lightly sprinkle zucchini with garlic salt and freshly ground black pepper. Use a small spoon to spread a thin layer of Parmesan cheese on each slice of zucchini. Bake for 15 to 20 minutes, or until Parmesan turns a light golden brown. (Watch these closely the first time you make them and pull them out of the oven early if the Parmesan is golden before 15 minutes!) Serve immediately.