In a large bowl, add the sliced mushrooms. Whisk together the marinade (tamari, oil, lime juice, cumin, paprika, and chili powder) in a separate small bowl. Pour the marinade over top of the mushrooms then toss until they are evenly coated. Set aside to marinate while you prepare the rest of the ingredients, or for at least 10 minutes.
Warm a grill or grill pan over medium-high heat. Add the mushrooms, peppers and onions then cook for about 2-3 minutes, on each side, until peppers are slightly tender but still crisp. Serve cooked filling with warm tortillas and desired toppings, and enjoy!
Calories do not include tortillas since that will vary greatly depending on the kind you choose. I like Siete Foods almond flour tortillas but they can be costly. If you can, try to find some made with whole grains for maximum nutrition.