Slice the portobello mushrooms and set them aside. Then slice the peppers and onion and place them in a large cast-iron skillet or wok with 2-3 tablespoons of water. Sauté until slightly softened, without overcooking, approx. 2-4 minutes. You want the veggies tender-crisp.
Then add the mushrooms and fajita seasoning and continue to sauté until the mushrooms are slightly reduced. Stir often. This will take approx 2-3 minutes.
Turn off the heat and add the lime juice, then mix to combine. Taste and adjust the seasoning or lime juice if needed.
Serve with corn tortillas and all your favourite toppings.
Notes
Do not overcook the vegetables. They taste best when tender-crisp and not too soft.Prepare additional toppings in advance so once your mushroom fajita filling is ready, you can enjoy them straight away.Keep leftover filling in the fridge, in an airtight container for 3-4 days, and reheat on the stovetop. Do not assemble the fajitas in advance or the wrap will get soggy.The nutritional information does not include optional toppings.