Heat oven to 220C/200C fan/gas 7. Toss the chips with the oil, 1 tsp chilli flakes and some seasoning. Arrange in a single layer on a large baking tray and cook for about 30 mins, turning halfway through.
Put the mince, remaining chilli flakes, onion, Parmesan, tomato ketchup and lots of black pepper in a large bowl and mix to combine. Shape into 4 burgers. Ten mins before the chips are ready, put the burgers on a baking tray and bake for 10 mins until cooked through.
Top one half of the buns with the lettuce, tomato and onion. Add the burgers, then top with the roll tops. Serve with chips and pickles on the side.