Mix all the ingredients for the marinade together: celery salt, paprika, lime juice, oregano, chilli powder, salt, pepper and oil.
Cut the steak into strips, add the steak to the marinade and leave for 30 minutes or longer if possible.
Cut the peppers in half and de-seed, then cut into thin strips roughly the same size as the steak.
Peel the onion and cut into similar sized strips.
Heat a grill or large frying pan on a high heat.
Add the steak, peppers and onions and fry while stirring for 4 minutes, longer if you like your steak well done.
Add to the tortillas, cover with sour cream and serve.
«You can use the same marinade for chicken or fish.»