Mix sour cream and lemon juice, season to taste with salt, pepper and sugar. Wash the dill, shake dry, pluck flags from the stems and chop finely. Stir the dill into the dressing. Crumble the pumpernickel finely.
Heat a pan without fat, toast bread crumbs crisply while turning.
Clean, wash and slice the zucchini. Grease a grill pan with oil, fry the zucchini in portions on both sides for about 2 minutes, season with salt and pepper. Remove from the pan.
Mix the salad with the zucchini and arrange on plates. Halve the trout fillets and arrange on the salad. Drizzle with dressing and sprinkle with breadcrumbs.