Mix in a shallow ovenproof dish:
chopped red onion
chopped fennel bulbs
salt, pepper, olive oil.
Roast in preheated oven (200ºC/400ºF) until soft. Lay over the vegetables:
a slab of white fish,
baste with the panjuices, sprinkle with salt and pepper. Cook for another 15 to 20 minutes. Serve over brown rice with a generous squeeze of lemon juice.