Clean and wash the salad, pluck into bite-sized pieces and drain. Peel radish and carrot. Peel the radish with a peeler and cut it lengthwise into thin slices. Chop the carrot into fine strips. Halve trout fillets lengthwise and cut them diagonally into pieces. Carefully mix oak leaf salad, radish, carrot and trout pieces and divide into 4 plates.
Wash the dill, dab dry well and cut finely. Mix mustard and lemon juice. Gradually add the oil. Stir in dill, except for a teaspoonful, and season to taste with salt and pepper. Pour the sauce over the salad and serve sprinkled with the remaining dill and coloured pepper