Substitute four 6-ounce skinless salmon fillets for the steak. Omit oil and sugar and do not brown salmon, carrots, and onion. Simply bring broth, carrots, onion, and potatoes to boiling; reduce heat and simmer, covered, 15 minutes or until just tender. Season salmon with salt and pepper; add to vegetables and simmer, covered, for 5 to 8 minutes or until just cooked through. Continue with step 4. Once spinach has been added to platter, stir 1 tablespoon of lemon juice into the simmering broth; spoon some over each portion of salmon and vegetables. Serve with mustard sauce and lemon wedges.