I'm not a big fan of low carb, however I am a fan of If-You-Don't-Miss-It-Skip-It! LOL The nice thing about swapping the tortilla for lettuce is it reduces the calories and gives you room for other things like extra cheese! Most of the time you don't really taste the tortilla anyway and it's simply a vehicle for the stuffing, and so using the lettuce instead is a perfect alternative! You just get all the wonderful flavors you love about a taco!
I liked the idea of keeping all the components separate and build each one as you eat it. I think it was easier than building them all at once.