Usually, I buy a fajita kit, which contains a seasoning mix, salsa (which I'm not a fan ... Taking only 15 minutes to prepare, here's the BBC Good Food recipe I used to make my vegetarian fajitas.
In a medium saucepan, heat the water to a simmer. Add the seasoning and the oil and mix well. Cut the beef slices into 3 pieces. Add the beef slowly, separating each slice. Stir to mix and separate ...