ok if not Mexican....
Mentioned on the other thread is Casa de Mateo, its about a block and a half around the corner from Stash Cafe on St. Francis Xavier - it'll do in a pinch for Mexican - not bad, but not fantastic.
There's Garde-Manger (not Mexican, but a crab shack meets mediterranean kinda place), also on Xavier, who's doing some interesting stuff - call ahead as this place is always full. Also turns into a lounge/club after dining time.
Giving an intersection, not just a street name will help us to locate where exactly you are staying.
That being said, you are lucky because we are talking about a short stretch of street. And THAT being said, the immediate area is kind of a dead zone for chow. You can perhaps schlep to Old Montreal, Chinatown, or upwards to Mile End.