Brown meat and add taco seasoning as you would for tacos. If you are not serving this right away refridgerate.  In a large bowl put lettuce,tomatoes, onion.  When you are ready to serve add meat, cheese ,Doritos and put as much Catalina dressing as you wish ,mix and serve.

Sometime I use a package of grape tomatoes cut in half.  I usually don't use the entire bag of Doritos.