For the banana fish, peel and finely chop the garlic. Wash the fish fillets, dab dry, sprinkle with a little lemon juice, rub with salt, pepper and garlic and fry in a little oil. Remove the fish from the pan.
Peel bananas and cut into slices. Drizzle half of them with lemon juice, sprinkle with a little salt and put on the fish, then keep warm.
Peel and finely dice the onion, brown it in the pan and deglaze with the fish stock. Stir in the tomato paste and add the remaining banana slices. Stir well again while bringing to a boil. Continue to simmer over low heat and add sour cream.
Add the fish fillets and let them simmer until done. Wash and pluck the basil leaves. Season the banana fish again with lemon juice, salt and pepper, garnish with basil leaves and serve.