Cook bacon in a large skillet until it is crispy, about 8 minutes. Remove with a slotted spoon and drain on paper towels, leaving bacon drippings in skillet.
Add asparagus and cook over medium heat until crisp-tender, stirring regularly. This will take you about 5 minutes for thin asparagus and closer to 10 for thick asparagus.
Stir in bacon, mustard and parsley, and stir for about one more minute until the mixture is fully combined and warm. Serve at once.