After the 15 minutes take a look and see if the asparagus is just about done cooking. You can tell when the tips are starting to look a bit crispy, the asparagus has shrunk in size and the side of the asparagus that is resting on the cookie sheet is looking a bit brown. When they reach this stage, sprinkle the cheese over all of them. Don’t worry about being neat, as it is okay if the cheese hits the pan. (In the picture you can see the asparagus ready for the cheese to be added.) Continue cooking for about 5 minutes.