Cook and drain spinach. Melt butter in a medium saucepan over medium-high heat. Add garlic; sauté 1 minute or until tender. Stir in spinach and parsley; gradually add Pernod, next 4 ingredients, and, if desired, salt. Remove spinach mixture from heat, and add Parmesan cheese.
Scrub oyster shells, and open; discard tops. Loosen meat, but leave it in the bottom shell. Make a bed of rock salt in a 15- x 10-inch jellyroll pan, and arrange oysters on the rock salt. Top oysters generously with spinach mixture. Bake at 450° for 10 minutes.
Alternate cooking method: Oysters may be cooked directly on a grill, covered, for 6 to 8 minutes.