Illegal Food Vendors

Hi,

I recently saw some posts on Facebook, (will not name the group here) where the home-cooked foods are being advertised to be sold. Usually, they range between 5 to 20 Euros, but there are some who even bake cakes for which they charge over 60 - 70 Euros. I have seen that these posts are mainly coming from communities belonging to Algeria/Lebanon/India.
I called one of them to enquire & found that they do not hold any registered company/license.
So, my question, is it even legal to sell foods here in Brussels (Belgium) without a license?
I see it as a red flag. It is both dangerous to health & also these people are avoiding tax.
I consider it as an illegal activity. Can such activities be reported to the authorities? If yes, how?