Slice the beef skirt steak into thin strips against the grain. In a bowl, toss the sliced steak with 1 tablespoon of olive oil and the fajita seasoning, ensuring it is well coated.

Heat the remaining 1 tablespoon of olive oil in a large skillet or cast-iron pan over medium-high heat. Add the sliced bell peppers and onion to the skillet and cook for 5-7 minutes until they are tender-crisp.

Push the vegetables to one side of the skillet and add the seasoned steak strips to the other side. Cook the steak for 3-5 minutes, stirring occasionally, until it is browned and cooked through.

Stir the steak and vegetables together to combine thoroughly.

Serve the hot steak and vegetable mixture in warm tortillas, topped with salsa, sour cream, and guacamole as desired.