Any opinions on the best?

Moved from Tech Support and tagged for Belgium

Sorry I can't help you with most of the vego restaurants, but just so you know - Belgian frites are fried twice in beef fat and most shops use this. One that doesn't is Frites Atelier in the Rue Ste.-Catherine, they use vegetable oil and some of the options are vegetarian (i.e. the toppings). They are pretty good frites there, you can't go wrong with them. They also have some beers on tap so you can have quite a feast.

There is also a restaurant, Le Perroquet, which specialises in pita bread sandwiches. I have not been there for quite a long time but they accommodate vegetarians quite well there. But in reality there will be heaps of restaurants. Try looking up Happy Cow for a curated list.

Lavandula

Not all beers are vegan/vegetarian so you should check those too.
Most restaurants have a couple of veggie or vegan dishes on the menu nowadays.
I'm not a vegetarian but I usually opt for those anyway.

Anyway a quick search, which you could also do to find others threw up:
https://humushortense.be/
https://www.visit.brussels/en/visito...od-in-brussels
That one is quite old now so you would need to check if they are still open.

And no doubt Trip Advisor has a more up to date list of places.