Tex/Mex restaurant

The only Tex-Mex I'd recommend in Brussels is Chez Wa Wa in Ixelles. It's run by an American, so is actually pretty good and is counter service with tables rather than a restaurant. Fresh ingredients and sensible prices. I saw that one had opened on the Quai des Briques last year, but no idea if it's any good.

Not Brussels I know - Leuven has New Mexico in Muntstraat. Food is good, but prices high. Also Donki, which is a Chipotle copy. El Sombrero is also nearby and online reviews are higher than the others, but I haven't been.

Otherwise I suggest you take a trip over to Aachen or the Netherlands where the Text-Mex is somewhat better and cheaper.

Forgot to add - whatever you do, don't set foot in Chi-Chis. It may say Tex-Mex on the outside, but it could not be further away.