Pre-heat the oven to 180 degrees (fan assisted). Peel the potatoes and then cut into chips with a crinkle cutter if you have one. Place in salted water and bring to the boil, then simmer for about 4 minutes. Spread onto a baking tray and spray generously with the low cal cooking spray. Place in the oven and bake for 30 minutes, tossing a couple of times during cooking.
Place the bread into a food processor and blitz into breadcrumbs. Then pop into a bowl and mix in the tablespoon of oil into the breadcrumbs gently with your hands. Next, break and separate the egg. Whisk the egg white until it is fluffy and forms peaks. Then whisk the egg yolk in a separate bowl and then fold into the egg whites.
Put a layer of foil on top of a baking sheet and lay out your fish fillets. Spoon the egg mixture gently on top of the fish and then sprinkle generously with the breadcrumbs (set the remaining breadcrumbs aside to use another time). Place into the oven and cook for 20 - 25 minutes until the fish is cooked through
Five minutes before the end, boil the peas in salted water for about 4 - 5 minutes until soft. Strain then add to a bowl with the butter and mash gently wth a potato masher until at the desired consistency.
Remove the fish and chips from the oven and serve with the mushy peas