What kind of guacamole are you eating??? Most of the guacamole I've made or entered into MFP has less than 2 or 3 net carbs for a generous serving. If you're making your own taco salads, I'd suggest trying to make your own guac, with mashed avocadoes, a little lemon juice, seasoning, and a little hot sauce instead of tomatoes. I don't think 1 Tbsp of most guac will ruin your diet. I ate taco salads from restaurants (so didn't control what they put in them) with guac and sour cream at least twice during my first week (and more than 1 Tbsp of each, for sure) and I lost 8 lbs. Everyone's different, though.
Also, avocadoes are really good for you because they have potassium, which is hard to get on a low-carb diet.