Preheat oven to 350.
Pour oil into small frying pan and heat to 3-4 (low/med-low)
Lightly fry each tortilla in the warm oil - be careful not to cook them through!
You can pass the tortillas through the enchilada sauce here, but I don't, because it's just so freakin messy doing it that way, and it doesn't really add anything.
Line the baking pan with a layer of oiled tortillas
Scoop chicken or beef filling into an oiled tortilla and lay them tightly into the baking pan
You can get 7-8 enchiladas across the 9" pan, and 3 rows along the 13" pan with 4" tortillas. Using 6" tortillas you can only get 2 rows with a gap, so put some sideways in the gap.
When the pan is full of rolled enchiladas, pour 2/3 of a can of enchilada sauce over them.
Sprinkle handfuls of cheese over the sauced enchiladas.
Mince / chop the onion.
Sprinkle the chopped onion and chopped black olives over the enchiladas.
If not baking immediately, cover with saran wrap before covering with foil.
Cover in foil (but not saran wrap!) and bake for 30 mins.
Remove foil and bake another 15-20 mins until cheese browns.