Trim the rhubarb. Halve and juice the lemons. Toast and roughly chop the walnuts. Crush the fennel seeds.
- 1 Cut the rhubarb into very thin slices – use a mandolin if you have one. Put the sliced rhubarb in a bowl and stir in the lemon juice.
- 2 Slice the radishes and celery very thinly and add to the bowl, along with the sugar, walnuts, half the oil, the fennel seeds and parsley. Stir to just combine, then set aside.
- 3 Heat the remaining oil in a large frying pan and add the seabass. Cook for 2-3 minutes, until golden, then turn over and cook for another 1-2 minutes, until the flesh is opaque and cooked through.
- 4 Serve with the rhubarb slaw and some crusty bread.