To make the salsa, simply mix the ingredients together in a bowl.
For the filling, thinly slice the onion. Seed and thinly slice the bell peppers.
Heat the oil in a wok or a large frying pan and stir-fry the onion and bell peppers for about 4 minutes, or until soft. Add the cumin and paprika and cook for 1 minute, then stir in the balsamic vinegar and boil until evaporated. Stir in the sugar and season with salt and pepper.
Warm the tortillas in a microwave or dry frying pan, then divide the fillings among them.
Start with the onion and bell peppers. Then spoon salsa and grated cheese on top. Finally, roll up your tortilla! Serve with sour cream.