Heat the oil in a frying pan over a high heat. Add the tortilla and fry for 1-2 mins on each side until crisping at the edges. Transfer to a plate.
Crack the egg into the pan and cook to your liking. Meanwhile, tip the beans into a bowl, season and add a squeeze of lime, then lightly mash with a fork.
Spread the beans over the tortilla, top with the egg, avocado, feta and chilli sauce. Squeeze over a little more lime juice just before eating.