This is a phrase that means “having a cactus in your face”. Its used to say someone looks very Mexican in his or her facial features, because we have a lot of nopales (an edible subspecies of cactus) here.
Soy Europeo – No mientas. Tienes el nopal en la cara/ I’m European- Don’t lie, you have a cactus on your face.
I hope you have learned something new, about the spanish that real Mexicans talk on their everyday life.
If you want to improve your Spanish, I also give tutoring lessons on skype using this page that host many teachers from all over the world, and while I don’t really do grammar, I can help with conversation and doubts about the language. Also, if you are interested in any language besides spanish, there are teachers and tutors for any language there.