Preheat your oven to 200°C/fan 180°C/gas mark 6. In a mixing bowl, toss together the tomatoes, onion and ½ tbsp olive oil. Tip on to a baking tray and cook in the oven for 15 minutes until softened and slighty charred. Tip into a bowl and add the balsamic vinegar. Stir and leave to cool.
Keeping the oven at the same heat, add 2 tsp oil to a large baking tray and heat for 2 minutes. Remove the baking tray from the oven, add the butternut squash chips and mix through the oil. Cook for 15 minutes, turn, and cook for a further 15 minutes or until cooked through.
Meanwhile, bring a large pan of water to the boil and add the potatoes. Cook for 8-10 minutes until tender. Add the peas during the last 3 minutes of cooking time and then drain, separating both. Mash the potato until smooth and set aside.
Put the milk into a pan and bring to the boil. Add the cod, take off the heat and leave, covered, for 10 minutes, turning over halfway through. Remove the fish from the milk and flake into a bowl. Add the mashed potato along with the peas and season. Shape the mixture into 6 ‘sausages’.
In a separate bowl, lightly whisk the egg along with 1 tbsp water. Dust the ‘sausages’ with the flour, then dip each one into the egg, followed by the breadcrumbs. Place a large frying pan over a medium heat and add 1 tbsp oil. Once hot, add three of the cod dogs and cook until golden brown, turning often. Drain on kitchen paper. Add the rest of the oil, then cook the rest of the cod dogs.
Toss the parsley with the cherry tomato relish. Line the hot dog buns with salad leaves and top with the fish dogs. Serve with the relish and butternut chips.