Bring 1 1/4 cups water and asparagus to a boil in a small saucepan. Stir in couscous and butter. Remove pan from heat; cover and let stand 5 minutes. Fluff couscous mixture with a fork. Grate half of cheese; stir into couscous with dill, pepper, and salt. Shave remaining cheese; sprinkle over couscous mixture.