Season steak and veggies:

Cup of Yum
1. Put the steak slices in a medium bowl and season with 1 tablespoon of the Worcestershire sauce, ¼ teaspoon of the salt, and a few grinds of black pepper. Stir to coat the beef. 
2. In a large bowl, combine the mushrooms, onion, and bell pepper. Season with the remaining 1 tablespoon Worcestershire, remaining ¼ teaspoon salt, and a few grinds of black pepper. Stir to combine. 

Cook the steak:

1. In a large cast-iron skillet, heat 1 tablespoon of the oil over medium heat. Add the steak and cook for 6 to 9 minutes, flipping the pieces to cook evenly. Transfer the steak to a plate and cover with another plate to keep warm. 

Cook the veggies:

1. Add the remaining 1 tablespoon oil to the skillet. Add the onion and bell pepper and cook, stirring frequently, for about 5 minutes. Add the mushrooms and cook for an additional 2 minutes, or until tender. Return the steak to the skillet and heat through for 2 minutes. Remove the pan from the heat. 

Make it cheesy:

1. Lay the provolone cheese slices over the beef and vegetable mixture and allow it to melt. 

Assemble:

1. Fill the taco shells with the cheesy skillet mixture and stir.