In a poacher or large roasting pan, combine the wine, peppercorns, and bay leaf with 1 cup of water. Bring to a boil, then reduce to a simmer. There should be about 1 to 1 1/2 inches of liquid in the pan.
Add the leeks and arrange the fish on top. Cover and simmer until the leeks are tender and the fish is opaque, 12 to 18 minutes.
Arrange the fish and leeks on a platter. Add salt and pepper and drizzle the vinaigrette on top. Garnish with lemon wedges and serve.