Trim any fat from steak and cut into strips. Sear, and place in slow cooker.
Chop onion, cilantro, and garlic; add to slow cooker along with salsa, lime juice, and seasonings.
Cover and cook on low for 5-6 hours.
Chop bell pepper and mushrooms. Add to slow cooker and cook for another hour.
Preheat oven to 250°F. Wrap tortillas in foil and bake until warmed through (or heat one at a time in a microwave if preferred).
Wrap fajita mixture in warmed tortillas and garnish with desired toppings.
Serve with your favorite fruit on hand.