Preheat oven to 400F. Slice each potato lengthwise into 1/4-inch ovals, then slice each oval lengthwise into matchsticks. Coat a baking sheet with 3 sprays of the vegetable oil. Combine the egg whites and Cajun spice in a bowl. Add the matchstick potatoes into the prepared baking sheet and spread them out into a single layer, leaving a little space between. Place the baking sheet on the bottom shelf of the oven. Bake for 40-45 minutes, until the fries are crispy, turning them every 6 to 8 minutes with a spatula so that they brown evenly. Serve immediately.
