TheFork users who ate in L'Isle-Adam have said really good things about La Bocca, La mia Storia and Tesoro Mio. Maybe you should give them a try!
Some of the more popular pizzeria restaurants that offer vegetarian options on their menu in L'Isle-Adam according to TheFork users include:
La Bocca, with a 9.6 rating
Tesoro Mio, with a 9.6 rating
La mia Storia, with a 8.7 rating