Melt butter; add crumbs and saute 1 minute, stirring constantly.
Soften the shallots and onions until golden.
Cook and stir spinach until wilted. Remove from the heat; Stir in lemon juice and pepper.
Add the pastis and half the oyster liquor (passed through a sieve) and bubble until reduced by half. Allow to cool a little.
Add shallot mixture and herb, garlic, spinach, green onions, parsley, lemon juice, butter, and Pernod to a food processor and pulse until finely chopped.
Then add the remaining butter and a good shake of Tabasco and pulse to combine.
Taste and add more hot sauce if necessary.
Arrange oysters in shells (or individual dishes).
Heat the grill and arrange the oysters on a heatproof platter covered in rock salt (this will keep them steady). Top each with a spoonful of the butter and flatten down to coat. Sprinkle with breadcrumbs. Bake, uncovered, at 450° until oysters are plump, 6-8 minutes, watching all the time, until the breadcrumbs are golden and the butter is bubbling.
Lemon wedges, for serving