In a large saucepan, heat the oil over a medium heat. Add the onions, celery and red pepper, cooking slowly until soft but not browned – for about 10 minutes.
Add the plum tomatoes, with their juice, along with the oregano and paprika, and break the tomatoes up a bit with a spoon. Simmer for 10 minutes, uncovered. Blitz with a hand held blender, blender or food processor until smooth.
For the pizza tacos:
Lightly char the tortillas on each side in a griddle pan, or warm them slightly in the oven. Spread the sauce on half of one side of the tortilla, top with mozzarella, sweetcorn, peppers and basil (or desired toppings) and place under the grill/broiler for a few minutes until the cheese melts. Fold and serve immediately.