Cut the monkfish into 8 equal chunks. Cut the cod fillet to give 4 pieces. Put the monkfish, cod and scallops into a bowl and add the garlic, rosemary, lemon zest, olive oil and some salt and pepper. Mix carefully, cover and leave to marinate in the fridge for 1 hour.
Heat a large pan over a medium heat and add a drizzle of olive oil. When it is hot, add the onions, garlic and red peppers. Cook, stirring occasionally, for 5 minutes until the vegetables have softened but not coloured. Now add the chilli flakes, orange zest, saffron, bay and rosemary and cook for 2 minutes. Stir in the tomato purée and cook, stirring frequently, for 5 minutes.
Add the drained chopped tomatoes, orange juice, celery and celeriac. Cook, stirring occasionally, for 10 minutes. Next, add the white wine and fish stock and simmer gently for 20 minutes. Taste and adjust the seasoning, if necessary.
Now add the monkfish to the stew base and cook for 1 minute. Next, add the cod, scallops, mussels and shredded brussels sprouts and cook for another 2 minutes. Finally, add the squid and chestnuts then cook for 2 minutes.
To make the rye bread croutons, cut the rye bread into ½cm cubes and heat some sunflower oil in a large frying pan. Once hot, shallow-fry the rye bread cubes until crispy then drain onto kitchen paper.
To serve, place the rye-bread croutons in serving bowls then serve the stew in the centre of the table for everyone to help themselves.