Preheat the oven to 200°C/gas mark 6. Place the potatoes in a bowl and toss with the olive oil. Transfer to a non-stick baking tray and bake in the oven for 40 minutes.
Meanwhile, scatter the breadcrumbs over a baking tray and bake in the oven for 2 minutes until golden. Remove and set aside.
Crack the egg into a bowl and beat. Place the flour on a plate. Pat dry the fish fillets using kitchen paper and coat in the flour. Dip into the beaten egg and then in the breadcrumbs to coat. Place on a baking tray and bake for 12 minutes, until cooked through.
Meanwhile, boil the frozen peas for 3-4 minutes. Drain the peas, reserving 100ml of the cooking water, and return them to the pan. Using a potato masher, crush the drained peas with the reserved water. Build the chips in stacks to create a tower and serve with the fish and crushed peas.