Combine mushroom ingredients and place WHOLE mushrooms stem side up on a baking dish with marinade for one hour. Grill each side for 4 minutes, brushing with the marinade every few minutes.
Wrap the tortillas in alumium foil and place in a 350 oven while you prepare the remaining ingredients.
Saute the onion and red pepper in a large skillet over high heat for 5 minutes. Add water 1 to 2 T at a time to keep the vegetables from sticking to the pan. Add the grilled mushroom strips, cumin, jalapeno pepper, garlic, cilantro, lime juice and salt and cook for another minute. Remove from the heat.
Serve the fajita mixture with the warmed tortillas, guac, salsa.