Last time I asked was one year ago, and AF offered the possibilty to preorder a vegetarian meal, only for flights longer than 2:30 hrs. I ordered them by phone as I could not see the option online. I found it so tasteless that I now prefer to play roulette and discover on board if I can eat the meal.
See an example of such vegetarian meal below: vegetable sandwich, layered fruits and a sort of a cream which was probably vegan.