TheFork users who ate in L'Haÿ-les-Roses have said really good things about Le Rustic, Amarone and Marou. Maybe you should give them a try!
Some of the more popular Salad restaurants that offer vegetarian options on their menu in L'Haÿ-les-Roses according to TheFork users include:
Le Rustic, with a 9.2 rating
Amarone, with a 9.4 rating
Marou, with a 9.5 rating