Fry sliced onion in frying pan with half the olive oil until golden, then remove.
Patties
While onion is frying, grate the carrot, parsnip, courgette into a mixing bowl (give the grated courgette a squeeze to release some moisture)
Incorporate mincemeat into vegetables and combine with egg using your hands.
Form four patties and fry in a hot pan with the remaining oil for about four minutes each side until cooked through.
Lay cheese slices, if using, on cooked side of patties whilst cooking otherside in the pan.
Toppings
While patties are cooking; shred lettuce and slice tomato.
Once patties are cooked, assemble burgers; swipe mayo on bottom bun, top with lettuce, tomato slices, cooked pattie, onions, ketchup and top with burger bun – enjoy!