Preheat the oven to Gas mark 6/ 200°C/Fan 180°C. Trim the asparagus down to remove any thick stalk (remove approx 5cm/2inches). Place into a roasting tin with the leeks and toss with the oil and season generously with salt and freshly ground black pepper. Toss in the Chinese 5 spice and lemon rind and toss well. Roast in the oven for 20 minutes until lightly charred in places. Remove and allow to cool a little.
Season the inside of each of the sea bass and make deep slashes in the top of each. Fill each with the roasted asparagus and leeks and tie with a piece of string to hold the filling inside the fish. Place into a roasting tin and drizzle over the lemon juice and press pieces of the lemon thyme into the slashes. Season well and cover with foil and roast in the oven for 15 minutes then remove the foil and roast for a further 15 minutes until the fish is cooked through and lightly charred in places.
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