Preheat oven to 375°F. Lightly coat two large baking sheets with cooking spray.
Use a mandoline to slice vegetables 1/16-inch thick. If using beets, sandwich slices between layers of paper towels and press firmly to remove excess liquid. Arrange vegetable slices in a single layer on the prepared baking sheets. Coat top of all of the vegetable slices with cooking spray; sprinkle with salt and pepper.
Bake for 10 minutes. Remove baking sheets from oven and let stand for 5 minutes. Return baking sheets to oven. Bake for 4 to 8 minutes more, removing baking sheets to check for doneness every minute after 4 minutes. Chips are done when the center of each chip no longer looks wet. Transfer chips to paper towels. Let cool for 5 minutes to crisp the chips.