Heat a large frying pan to a medium high heat and add a large knob of butter. When foaming add the split muffin and toast for 1 minute, turning half way through. Remove from the pan and set aside.
Turn the heat down to medium low, add a large metal cooking ring to the pan and spray well with oil. Crack the egg into the ring and pierce the yolk. Add a large splash of water to the pan and then cover with a lid and cook for two minutes.
Remove the ring and put the egg onto the base of the muffin. Add a slice of cheese, season with salt and pepper and finish with the muffin top. Wrap with greaseproof paper and freeze for another day if not eating right away.