A: I start with a small bowl of black bean or tortilla soup. To keep from devouring all the guacamole and a million chips, I ask the server to skip the chips and bring me one soft corn tortilla instead. Then I eat just enough guac to cover the tortilla.
For an entree, fajitas are great, but you have to pick your battles: Rice or tortillas? Sour cream or guacamole? Beans or cheese? And, even then, I don't eat every last bite.