TheFork users who ate in Montmorency have said really good things about Au 2 Saint, Le Loft and Accattone. Maybe you should give them a try!
Some of the more popular Pizza restaurants that offer vegetarian options on their menu in Montmorency according to TheFork users include:
Au 2 Saint, with a 9.1 rating
Le Loft, with a 9.4 rating
Accattone, with a 8.8 rating