Heat oven to 200C/fan 180C/gas 6. Toss chips in oil. Spread over a baking sheet in an even layer, bake for 40 mins until browned and crisp. Put the fish in a shallow dish, brush lightly with oil, salt and pepper. Sprinkle with half the lemon juice, bake for 12-15 mins. After 10 mins sprinkle over a little parsley and lemon zest to finish cooking. Meanwhile, mix the capers, yogurt, remaining parsley and lemon juice together, set aside and season if you wish. To serve, divide the chips between plates, lift the fish onto the plates and serve with a spoonful of yogurt mix.