I don't know Taco John's, but I did google it and it seems they have nutritional information online.
http://www.tacojohns.com/images/data...ition_Info.pdf
Getting a chicken softshell taco for 190 calories doesn't seem so bad. There are moderately healthy choices at almost every restaurant. Just because your boss chooses a particular restaurant doesn't mean that s/he can choose what your meal will be.
Can you bring breakfast and pack a lunch so that you don't feel stuck? Like even if your boss pops into a place to grab something, you can just say no thanks because you have your food in hand. Sometimes people just want to sit with you and eat, no matter what you're eating. If coworkers order meals out, I will often sit with them and eat my own food.