Cut the beef into bite-sized pieces.
Slice the onion and bell pepper into thin strips.
Heat cooking oil in a pan and stir-fry the beef.
Season the beef with salt and pepper.
Add the onion and bell pepper and stir-fry together.
Warm the tortilla in a pan.
Place the stir-fried ingredients on the tortilla.
Add cheese and sauce as desired.
Roll up the tortilla and serve on a plate.