Use a spoon to scrape off the gills from the portabella mushrooms and slice into long thin pieces.
In a large skillet, heat the oil over medium heat. Once the oil is hot, add the onion and jalapeños. Sauté for 5 minutes. Add garlic and cook for 30 seconds.
Add mushrooms to a bowl and toss with 1 tablespoon of oil, a sprinkle of lime juice, and taco seasoning.
Raise the skillet heat to medium high and add the mushrooms. Cook, stirring only occasionally, for about 10 minutes.
Warm the tortillas. Add mushroom filling inside each tortilla and desired toppings on top. (See recipe notes for topping ideas.)
Mushrooms: Portobello mushrooms are preferred for tacos as they are “meatier” in texture, where cremini mushrooms get really soft when cooked.Grilled Mushroom Tacos: leave the portabellas whole, and no need to remove the grills. Prepare as directed above and grill over medium high heat for 4-5 minutes on each side. Then slice into strips for serving.