If you pick a buffet options, you will have lots of vegetarian choices
Or sit down restaurants ( Blue lagoon, walt, auberge, disney village...)
In the burgers places , it's a shame they do not offer a fish burger!
You can only find beef / chicken options...
Let's be honest the salads at quick service places are really not good!
France like some other European countries think that all végé eat fish so will be often offered it, same as ham on salad as they don't see it as meat. It's got better but there is still a long long way to go