How to Make It
In a medium bowl, combine the onion, vinegar, and ¼ teaspoon salt. Let sit, tossing occasionally, until softened, 30 to 60 minutes.
In a small bowl, mix together the yogurt, dill, and ¼ teaspoon each salt and pepper.
Serve the trout with the bread, yogurt sauce, pickled onions, cucumber, and lemon wedges.