Heat the oil in a pan and then slowly whisk in the flour and fajita seasoning.
Gradually add the stock and passata, stirring well.
Reduce heat and simmer for 10 minutes.
If you like your enchiladas really spicy, then feel free to add an extra teaspoon of chilli powder to the fajita seasoning, or you could stir a spoon of chipotle paste in to the sauce whilst it is cooking. American chilli powder is a lot milder than what we get here in the UK, so bear that in mind.
Add a pinch of cinnamon for an extra burst of flavour.
You can batch cook this sauce and it will freeze well. Let it cool and then portion it out in to freezer bags and it will keep in the freezer for a couple of months.
To make this sauce gluten free, make sure you use gluten free flour and stock.