For the poaching liquid, fill a large straight-sided skillet with a tight-fitting lid halfway with water. Add peppercorns, parsley, dill, onion, celery and bay leaf. Squeeze lemon juice into pan and add wedges. Cover and bring to boiling, season with salt to taste. Reduce heat to low and simmer 20 minutes.
Meanwhile, for the salsa, in a medium bowl combine cucumber, bell pepper, scallion, dill, lemon juice, and salt and pepper to taste. Cover and refrigerate until ready to serve.
After the poaching liquid has cooked 20 minutes, increase heat to high and bring to boiling. Reduce heat to low and add the fillets. Cook, covered, 5 minutes or until fish flakes easily with a fork.
Remove fillets from poaching liquid. Place on a serving platter, top with salsa and serve.