Ok there is the Jiminy Cricket Menu in the California Grill with three vegetarian choices for each course. In Walt's there is a complete vegetarian menu, too.
We stayed away from the fast food. Once bought a farfalle salad in the Bella Notte, but it was not worth the money. Tiny portion in a plastic box from a food company. Save your money and go to one of the table service restaurants. It is not as expensive as you might think because in Paris you will hardly find a good menu for under 25 Euro. If you are a shareholder or if you have an annual passport you will ge a reduction too.
There is an italian restaurant in the shopping center just one metro station away and there are lot of other choices for veggies, too. There is very large supermarket with more choices you can imagine. I even found "traditional mousse o chocolat" without gelantin
.Generally in most of the restaurants there is a minimum of one vegetarian menu/dish witch is marked with a symbol, even in the King Ludwig's. Mots of them have vegeatrain menus. We stayed 14 days as ovolactovegetarians in DLP and nether had a problem. Ok sometimes they mark fish as vegetarian, too.
If you go for a day trip to paris go to the La Victoire Suprême du Coeur
41 rue des Bourdonnais, 75001 PARIS 1er. It is near "Les Halles" and it is 100% vegetarian. It was a new experience for us not to be in the minority

. Never felt so "normal". (I am a vegetarian for 22 Years even in the army).
Greetings
kaido