If you like fajitas, there is a place called Fajitas on I-17 that is yummy. Exit at Dunlap, stay on the frontage road and it will be on your right about 1/2 mile up.
If you want really, really good Mexican food close to the airport try Ranch Market at 16th Street and Roosevelt. It is a grocery store in front, but on the west side of the building there is a table service restaurant that is awesome and it is very close to the airport and rental car places. If you land hungry, it is really good.
If you do not want Mexican food - my other all time favorite place was on Man vs. Food - Chompies. From the airport get to Highway 51 and go north to Cactus - turn right and it will be by the Paradise Valley Mall. From there you can get back on Highway 51, continue north to the 101 and hook up with I-17 to continue north to Grand Canyon.