My favorite food truck in Brussels is definitely Chang Noi.
I first tried them, last year, at the Food Festival in Brussels and have been following them ever since. Not in the stalking way but the I-need-some-of-your-food-or-I-will-die way.
The spicy raw shrimp bites are my favorite. The burst of spicy flavors topped with a mint leaf is superb.
You can join their FB page and see their schedule https://www.facebook.com/ChangNoiCuisine