In a large saucepan over medium heat, melt butter. Mix in flour and whisk constantly 2 to 3 minutes, until a thick paste-like roux has formed.
Stir file powder, garlic, spring onions, onions and green capsicum into the roux. Cook and stir until tender, about 10 minutes. Stir tomatoes into the mixture. Season mixture with black pepper, cayenne pepper, allspice, cloves, salt and bay leaf. Cook, stirring occasionally, until the mixture is well blended, 10 to 15 minutes.
Pour in mushroom stock and mix in rice. Increase amount of stock to cover all ingredients, if necessary. Bring to a boil and mix in snapper. Cover, reduce heat and simmer 1 hour or until rice is tender.