Pat fish dry with paper towels. Season fish and vegetables lightly with salt and pepper. In bottom at steamer, combine 1 inch water, lemon juice, parsley, peppercorns, and bay leaf. Bring to a boll.
Separate onion slices into rings. Place half on steamer rack. Place fish on onions. Cover with vegetables and remaining onion. Reduce heat to simmer, cover and steam until fish begins to flake, about 10 minutes per each inch of thickness.
Transfer fish and vegetables to warm platter. Serve hot.
Cajun Country -- New Iberia, Louisiana