Another trick is to get something like tacos and not eat the tortillas (or if it's a plate of 2-3 tacos, eat just one tortilla). You can eat the filling with a fork.
Also, at some Mexican/TexMex restaurants the nutritional info includes all the sides that come with an order -- like guacamole and sour cream. I know guacamole is a good fat but I don't really like it that much so I always pass it up.
Lastly, check out the "side orders" section of the menu. Sometimes you can put together a nice little meal taking from there.
If you're sitting inside and the AC is blasting, the soup might be nice!