Preheat oven to 425°F. Make lemon compound butter: Whip butter with a rubber spatula until fluffy, about 1 minute. Add lemon zest and juice. Mix well.
Gently saute fennel in oil until soft. Add garlic and chile flakes and saute another 45 seconds, without browning. Add spinach leaves, celery leaves, and watercress. Toss until spinach begins to wilt. Add the Pernod to deglaze. Allow mixture to steam until spinach is just cooked, adding more Pernod if needed to keep the pan moist.
Remove spinach mixture, leaving juices in the pan. To cool and drain, place spinach mixture on a clean towel set over a bowl, and put in the refrigerator.
Simmer pan juices until almost gone; set aside.
Once spinach mixture is completely cooled, squeeze out and discard excess liquid. Pulse in a food processor with the reduced pan juices, scallion, and parsley until well-chopped but not pureed. Stir in breadcrumbs by hand, adding salt and pepper to taste.
Arrange the rock salt or dried beans on a baking pan and warm in oven about 15 minutes. Meanwhile, shuck the oysters and place them on a separate pan of rock salt (this will keep them upright and prevent the juices from spilling out).
Put a dollop of lemon butter on top of each oyster, then a piece of bacon, a dollop of spinach mixture, another tiny dollop of lemon butter, and then sprinkle with herbed panko.