Steam potatoes and carrots for 15 minutes, add zucchini and steam for additional 10 minutes or until desired texture is reached.
Bring poaching ingredients (water, lemon juice, lemon peel, onion, parsley, and bay leaf) to boil in a broad shallow pan or skillet.
Simmer 5-10 minutes to extract flavor from seasoning.
Add fish. Simmer, partially covered, 10 minutes, or until fish flakes with a fork.
Remove fish with a slotted spatula and drain. Place on serving plate, surround with potatoes and vegetables.
Spoon Mustard-Dill Sauce over all, serve any remaining sauce on the side.