Cut the fish into portions and season with salt and pepper. Halve the tomatoes, remove the seeds and dice into small pieces.
Cut the leek into rings, peel the celery and chop into small pieces. Peel and grate the ginger. Heat the oil in a pan and fry the spices. Add the ginger, tomatoes, leek, celery and lentils and sauté briefly .Sprinkle with flour, stir and deglaze with the soup. Cover and simmer over a low heat for approx. 15 minutes, stirring occasionally and adding a little liquid if necessary. Add the spinach to the vegetables, place the fish on top and cover and leave to simmer for 10 minutes. Remove from the pan, stir in the yoghurt, season with salt and pepper to taste, return the fish to the pan and heat everything briefly