Preheat oven to 350 degrees. Lightly grease a small casserole dish.
Melt butter in a skillet over medium heat. Add oysetrs and cook for just a minute or two to get them about halfway cooked. Remove from heat.
Place cream cheese, mayonnaise, sour cream, and lemon juice in a large bowl. Mix together with a wooden spoon or a hand-held mixer.
Add spinach, green onions, Parmesan cheese, garlic powder, Worcestershire sauce, salt, TABASCO sauce, black pepper, and Pernod.
Add oysters, chopping them in half if they are large. Gently stir everything together.
Transfer mixture to prepared casserole dish. Bake for 20 to 25 minutes, or until bubbly.