Grate the red onion or blitz and add to a bowl
Finely chop the fresh parsley and mint and add to the same bowl
Add the egg, breadcrumbs, beef mince and seasoning to the bowl and mix until well combined
Take about a tablespoon of the mixture and flatten, place a cube of Kefalotyri in the middle, and roll the mince into a ball to cover, smoothing the edges to form a flat burger shape
Repeat with the remaining mince meat to form 10-12 burgers
Heat oil in a frying pan over high heat for 2 minutes until heated (test by poking a wooden spoon in the oil to see if it fizzes)
Carefully place the burgers in the hot oil
Cook for 3-4 minutes on both sides (7-8 minutes total) until crispy and golden
Place the cooked burgers on a plate lined with kitchen roll to drain excess oil
