Situated just in front of the Central Station of Brussels, Oats Day Long is what you are looking for a quick breakfast before taking the train or a (vegan and/or normal) coffee to go. They have several gluten free options (but they cannot guarantee that the dishes are 100% gluten free, because they are made in a facility that process gluten). They have lactose free and vegan options as well in their menu (where all allergens are written). I tried the Salted Caramel Pancakes. They were really good. I took as well a flat white (made with oat milk).
— Somewhat
— Gluten-free items are marked on the main menu
— Some
— Good