Drain the oysters in a sieve and collect all the oyster liquor. Pour the oyster liquor plus enough chicken stock to make three cups of liquid total into a saucepan. Bring it to a boil and lower to a simmer.
Combine the butter and flour in another, large saucepan and make a medium dark roux, stirring constantly. When the roux is the right color, remove the pan from the heat and add the green onions, stirring until they become soft--about a minute.
Add about a half-cup of the oyster water-stock mixture to the roux and stir lightly until just combines--about five seconds. Add the wine, Worcestershire, steak sauce, and lemon juice. Return to a simmer over low heat.
When you see the first bubbles return, add the remaining stock to the roux mixture and stir with a wire whisk until uniformly blended. Cook for about ten minutes, or until the sauce is thick enough to coat the back of a spoon. Add salt and pepper to taste. The sauce is now complete. You may do it ahead up until this point and hold it (refrigerated if it will be longer than an hour) until serving time.
When it's time to serve, bring the sauce to a simmer and add the oysters. With a big spoon, stir them into the sauce to avoid breaking them. Bring the sauce back to a simmer and cook until the oysters are curly at the edges.