I favor two approaches:
* Add individual, novel ingredients to a standard taco bar like corn relish alongside salsa or chive blossoms alongside chopped onions.
* Transmute the entire concept to a different cuisine.
Tortilla -> naan
Ground beef -> chicken tikka
Cheese -> paneer
Sour cream -> yogurt or raita
Mexican chili powder -> Indian red or green masala, shadrasa masala, etc.
Cilantro stays the same
Additionally, a taco bar can be as healthy as the ingredients. You can put almost any vegetable on a taco. Some, like eggplant or mushroom, will substitute for meat. Beans + rice = complete protein. Lots of fermented live foods such as pickles, yogurt, and cheese work great. It's basically just a salad in a bread wrapper.
Use your imagination. Fusion cuisine is one of the few cultural exchanges we haven't fucked up.