To make the mash, peel the potatoes and cut into even sized chunks. Put in a large saucepan and cover with cold water. Bring to the boil and cook for 12-15 minutes until very tender. Drain the potatoes in a colander and leave to stand for 2 minutes. Tip back into the saucepan. Mash the potatoes with the sunflower spread until smooth. Add the Free >From cheddar style spread and mix until smooth and creamy. Season with 1 tsp salt and some freshly ground black pepper. Set aside. To make the pie filling, pour the soya milk into a large non-stick frying pan. Add the onion, bay leaf, thyme and lemon zest and bring to a gentle simmer. Carefully add the fish and turn off the heat. Leave to stand for 6 NJ minutes or until the fish is just cooked. Remove the fish from the pan with a slotted spatula and place in a large mixing bowl. Pour the poaching liquor through a fine sieve into a jug and set aside. Discard the onion, herbs and lemon zest. Preheat the oven to 190C/fan 170C/ Gas 5. Melt the 75g sunflower spread in a large non-stick saucepan. Add the plain flour, mix well and cook over a low heat for 1 minute, stirring constantly. Gradually add the infused soya milk, stirring constantly between each addition. Bring to a simmer and cook for 2 minutes, stirring regularly until smooth and thick. Stir in the chopped parsley and prawns. Flake the fish into chunky pieces and scatter over the bottom of a 1.5 litre shallow ovenproof dish. Pour the parsley and prawn sauce over the fish. Top with the mashed potatoes, working your way around the sides of the dish before heading into the middle. Bake for 30 minutes or until the filling is bubbling and the potato topping is golden.