Combine 2 Tbs. butter and flour in a saucepan and cook over medium-low heat for about six minutes, to make a blond roux. Whisk in the chicken stock to make a veloute. Bring to a simmer and cook for about five more minutes.
Wash and pick the stems from the spinach. With the water clinging to it, put it in a heavy saucepan over medium heat until it wilts completely. (Better: steam it.) Remove and squeeze dry, into a ball.
Heat the remaining 1 Tbs. of butter in the same saucepan you cooked the spinach in, and cook the green onions until tender. Stir in the spinach and cook until well blended with the onions.
Remove the spinach mixture and chop it very fine in a food processor. Add the chicken veloute and the Pernod, process to mix well, and return it to the saucepan. Cook over low heat until all liquid has been absorbed. Remove from the heat and allow to cool. When lukewarm, stir in the egg yolks.
Beat the egg whites until they form stiff peaks. Stir about a fourth of the beaten whites into the spinach mixture. Then, with a rubber spatula, fold in the rest of the egg whites (streaks are okay).
Butter the inside of either one large soufflee dish or six six-inch ones. Spoon in some Parmesan cheese, and shake it around to roughly coat the sides. Shake out the excess. Load in the spinach mixture to within an eighth of an inch from the rim.
Bake the soufflees in the preheated 375-degree oven for about 40 minutes, or until browned on top. Refrain from opening the oven door for the first 15 minutes.
While the soufflees are in the oven, make the hollandaise sauce and keep warm. Poach the oysters in a little water for about two minutes. Drain them well, chop them, then stir into the hollandaise.
Get everyone at the table as the soufflees are coming out of the oven. Serve them immediately, and spoon the sauce into the center, punching a hole first so the sauce can fall to the bottom.