Brown the chicken and sausage
Warm the olive oil in a large saucepan over a medium heat. Add the chicken and smoked sausage, brown them on all sides, then transfer them to a plate and set aside.
Soften the vegetables
Add a little more oil if the pan looks dry. Stir in the onion, celery and pepper, then cook until softened, stirring regularly.
Add the aromatics
Add the garlic, Cajun seasoning and thyme. Stir continuously just until fragrant, taking care not to let the garlic burn.
Cook the flour
Stir in the flour and cook, stirring frequently, until it begins to turn brown. Return the chicken, sausage and any resting juices to the saucepan.
Simmer the gumbo
Pour in the chicken stock, using about half the quantity when the okra is omitted. Add the chopped tomatoes and okra, if using. Bring to the boil, reduce the heat, cover and simmer until the chicken is cooked through and the gumbo has thickened.
Cook the prawns
Stir in the king prawns and cook for a few minutes until they are pink, opaque and just cooked through. Season the gumbo with salt and freshly ground black pepper.
Garnish and serve
Ladle the gumbo into bowls, scatter over the chopped spring onion and serve with lime wedges for squeezing.