TheFork users who ate in Utrecht have said really good things about Seven, Fort de Gagel and Bij Moov. Maybe you should give them a try!
Some of the more popular Dutch restaurants that offer vegetarian options on their menu in Utrecht according to TheFork users include:
Seven, with a 7.9 rating
Fort de Gagel, with a 8.8 rating
Bij Moov, with a 8.8 rating