Preheat the oven to gas 6, 200°C, fan 180°C. Put the salmon fillets in a pan of boiling water and simmer for 5 minutes, until cooked through. Remove salmon from the pan and flake into pieces.
Meanwhile, place the potatoes in a pan of cold water and bring to the boil then simmer for 12-15 minutes, until softened. Drain, then mash and gently stir through the flaked salmon, dill, parsley and spring onions. Shape into 8 patties and dust with flour.
Dip the patties into the egg and then in the breadcrumbs until lightly coated. Heat 1 tbsp of the oil in a large frying pan and cook the fishcakes for 2 minutes each side, until golden. Place on a baking tray and cook in the oven for 15 minutes.
Heat the remaining oil in the pan and cook the spring greens and peas for 5 minutes, adding the garlic for the final minute.
To make the horseradish cream, combine the crème fraîche, horseradish and lemon zest in a small bowl. Serve with the fishcakes and green vegetables.