Heat the oil in a frying pan and cook the onion for 4-5 minutes until soft. Add the bacon and cook for a further 3-4 minutes or until it begins to turn a golden colour.
Remove the pan from the heat and transfer the bacon and onions into a large bowl.
Add the mashed potato and cooked vegetables, season well. Add the cheese, mix well and divide the mixture into six portions.
Using your hands, shape each portion into a cake. Put a little flour on a plate and coat each cake in flour on both sides.
Put onto a greased baking tray and brush with a little melted butter. Bake in a preheated oven (200°C / 400°F / Gas Mark 6) for 25 minutes or fry on both sides until golden brown.