Steam fish in the wine for 7 minutes (allow 12 minutes if frozen), then remove & add the mussels. Steam until the shells open. Reserve the wine. Steam or microwave the spinach leaves until they are just beginning to wilt.
Break or cut the cooked fish into bite- sized pieces & remove the mussels from their shells. Place them in a serving bowl with the lettuce, spinach, parsley & chives.
Use the wine used to steam the mussels & fish to make a dressing with the mustard & olive oil. Toss with the other ingredients while they are still warm.