Pre-heat the oven to 200°C/180°C fan/gas 6. Wrap the potato in foil, place on a baking tray and roast in the oven for 1 hour or until tender. During the last 10 mins, wrap the fish in foil, add to the tray and continue cooking for 10 mins until opaque and cooked through.
Once the potato is cool enough to cook, halve it and scoop out the filling. Flake the fish, removing any bones and discarding the skin. Add to a medium bowl with the peas, parsley, cheddar and egg. Mix together until combined.
Line a baking tray. Shape the mixture into golf ball-sized dollops and arrange on the tray and chill in the fridge for 30 mins.
Reheat the oven to 200°C/180°C fan/gas 6. Transfer the tray of fish pie bites to the oven and bake for 15 mins or until golden and cooked through.