Preheat the oven to 220C/Gas 7.
Arrange the fish fillets on a non-stick baking sheet and season with salt and pepper. Cut four slices of lemon and arrange one on each fillet. Scatter over the chopped parsley, drizzle with the oil and roast for 6 - 8 minutes until cooked through.
Meanwhile, cook the peas in pan of boiling, salted water for 4 - 5 minutes until piping hot. Drain well then place in a food processor with the creme fraiche and chopped mint. Whizz to form a coarse puree.
Divide the puree between four plates and place a cod fillet on each. Squeeze the juice from the remaining lemon half over the fish and serve.
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