For the tortilla: In a small bowl, whisk together all the tortilla ingredients and set aside whilst you heat a large non-stick frying pan sprayed lightly with oil and preheat your broiler (put the oven rack in the top third of the oven).
Pour the mixture into the frying pan, reserving about 1 tbsp of it (this is so you can use it to repair any cracks that you might get in the tortilla later). Cook until golden brown, and use a metal spatula (I used one of those ones that are supposed to be for frosting cakes) to GENTLY loosen the edges of the tortilla all the way around. Then using the spatula, again gently and carefully, slide it under the tortilla so that it's loosened from the bottom of the pan. (if you make any cracks, pour a little of the reserved mixture into it to seal it back up).
Put the pan under the broiler for 2-3 minutes until you can see that the tortilla as kinda shrunk and is a little bubbly. If you want, you can then flip it and gently fry it again to make this side golden brown too. Set aside on a piece of foil.
Place your choice of fillings down the center of the tortilla and wrap up. Wrap tightly in the foil, then either put it into the fridge for the next day or put it into the oven at 400F for 5 minutes (this sets the shape of the tortilla so that it doesn't unwrap and spill fillings allll over your hands). If reheating the next day, then place into a 400F oven for 10-15 minutes.