If you've got shells on your prawns, peel them and keep the heads and shells aside for your stock. Heat a large pan over a medium to high heat and add a lug of olive oil and your sliced sausages. Let them get some nice colour. While that's happening put a large stock pot on a high heat, add another lug of olive oil and fry any prawn heads and shells for about 5 minutes. Use a rolling pin to bash them up in the pot and release all their lovely flavours, then pour in your chicken stock, bring to the boil, and leave to simmer for 20 minutes.
Move your cooked sausages to a plate and add the flour to the fat left behind in the pan. Turn the heat down to low and stir. You want the roux to have a semi-loose, doughy consistency, so add a splash of olive oil if there isn't a lot of fat. (You also want the roux to get really nice and dark, so have a bit of patience and keep stirring to stop it sticking. It might take around 10 minutes to get it to the right darkness. Peanut butter colour is a good starting point, but you can take it even darker if you prefer by stirring and cooking it for another 20 to 30 minutes.) After about 2 minutes, add a splash more olive oil to the roux along with the holy trinity of onion, peppers and celery. Stir and cook for about 5 minutes, then scrunch up your bay leaves to help bring out their flavours and stir these into the trinity mixture with the thyme leaves. Fry for 5 minutes, then add your garlic, cayenne, Tabasco and the okra, which will act as a brilliant thickening agent. Give it all a good stir and fry for a couple of minutes.
At this point, add your stock. If you've got prawn shells in there, strain it through a large sieve. Stir and bring everything up to the boil. Add your crab claws, if using, and tinned tomatoes and simmer for 5 to 10 minutes. Stir in your cooked sausages, peeled prawns and crabmeat, and leave on a medium heat to tick away for another 5 minutes.
Have a taste and add salt and pepper and a good squeeze of lemon juice if you think it needs it. Keep tasting and seasoning until it's got some kick. Roughly chop the parsley and sprinkle into your gumbo. This is lovely served in bowls over some rice, but you can also put that wonderful big pot right in the middle of the table and let everyone go fishing. What a celebration!