You can channel destructive waves of energy, like those created by the dragons you emulate. When you take the Attack action on your turn, you can replace one of the attacks with an exhalation of draconic energy in either a 20-foot cone or a 30-foot line that is 5 feet wide (your choice).
Choose a damage type: acid, cold, fire, lightning, or poison. Each creature in that area must make a Dexterity saving throw against your ki save DC, taking damage of the chosen type equal to two rolls of your Martial Arts die on a failed save, or half as much damage on a successful one.
At 11th level, the damage of this feature increases to three rolls of your Martial Arts die.
You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest. While you have no uses available, you can spend 2 ki points to use this feature again.