Wash the lettuce in cold water, pluck it into bite-sized pieces and drain in a colander. Peel the onion and cut into fine cubes. Cut the chicken breasts into 1 cm wide strips and season with salt, pepper and curry. Wash the apples, quarter them, remove the core and cut into slices.
Put the onion in a non-stick pan in oil and let it glaze over. Add the chicken breast and apples and continue frying for 2 minutes over high heat. Set aside and let cool down a bit.
For the dressing, mix the mustard, vinegar, yogurt, apple juice, sugar, salt and pepper together in a large bowl. Put the iceberg lettuce in the bowl and mix with the dressing. Possibly season again to taste. Arrange on plates and spread the chicken breast and apple mixture over them.