Trim all visible fat from the pork fillet. Cut the pork widthwise into slices, about 5cm thick, then cut each slice into thin strips.
To make the marinade, put the lime zest and juice (reserving 2 teaspoons of juice for the salsa) in a shallow dish with the sugar, oregano, cinnamon and cayenne pepper. Add the pork strips and toss to coat, then leave to marinate while you prepare the rest of the ingredients.
To prepare the salsa, combine the tomatoes, onion and cucumber in a bowl. Whisk together the olive oil and reserved lime juice from the marinade with a little salt and freshly ground black pepper in a bowl. Drizzle the lime–oil mixture over the vegetables, add the chopped coriander and mix well. Cover and set aside.
Heat the vegetable oil in a frying pan or wok until very hot. Add the marinated pork and stir-fry for 1 minute, then add the sliced onion and stir-fry for a further 3 minutes. Reduce the heat a little, then add the capsicums and cook for a further 3–4 minutes until the pork is cooked through and the vegetables are tender.
Meanwhile, gently warm the tortillas in a microwave oven for 1 minute or following the packet instructions. (Alternatively, they can be warmed in a stack, wrapped in foil, in an oven preheated to 180 degrees C for 10 minutes.)
Spoon the pork and capsicum mixture into a warmed serving bowl and take it to the table with the tortillas, salsa and sour cream for diners to assemble themselves. Spread a little salsa over each tortilla, then pile on some of the pork and capsicum mixture. Add a spoonful of sour cream, sprinkle with a little paprika, then fold over or roll up to eat. Be sure to provide serviettes.