Is it possible to cure erectile disfunction through a vegetarian plant based diet?

Unlikely: The only way i could see that helping is if your ed is due to narrowed arteries in the area (unlikely at your young age) and you drop the fatty diet for a number of years, your arteries may clear out a bit allowing improved blood flow.

Improvement yes: Vegetarian, plant based diets are in general very good for your health, especially improve your hormonal function as well as result in fat loss in the abdominal area which plays a major role in reducing testosterone levels and causing low sex drive. So following a healthy, vegetarian based diet, and drinking plenty of water and avoiding processed starch and sugar, ed symptoms will improve a lot.