Preheat the oven to 200ºC, fan 180ºC, gas mark 6. Place the salmon, lemon zest, mixed herbs and sweet potato cubes on a baking tray. Drizzle over the olive oil and mix well.
Cook in the oven for 15 minutes, then remove the salmon and return the tray to the oven for a further 20 minutes.
Meanwhile, place the potato in a pan of cold water, bring to the boil and simmer for 10 minutes, until soft. Drain and mash with the milk.
Preheat the grill to medium-high. Flake the salmon into pieces, then gently mix with the mash. Shape into 12 fish fingers. Dip each into the flour, followed by the egg and then the breadcrumbs.
Place on a baking tray and grill for 10 minutes, until the breadcrumbs start to turn golden.
While the fish is grilling, boil the peas for 2 minutes. Drain and serve with the fish fingers and sweet potato cubes.