This recipe from Kraft Foods is a great option when it's 5 o'clock and you still have no clue what you're going to make for dinner.
We almost always have all these fixings on hand. Just serve the cheese on the side for those in your family who can eat it and make sure the taco seasoning mix you use is MSPI-friendly -- I use Ortega.
Also, stretch your family's food budget by adding a can of corn and/or black beans. The leftovers can be used to make enchiladas or burritos.