TheFork users who ate in Essen have said really good things about Pierburg - Erika Bergheim, Lujo Seecafé & Restaurant and UNVERHOFFT. Maybe you should give them a try!
Some of the more popular Creative restaurants that offer vegetarian options on their menu in Essen according to TheFork users include:
Lujo Seecafé & Restaurant, with a 9.1 rating
UNVERHOFFT, with a 9.3 rating
Dui Sushi - Bochum, with a 9.6 rating