How to Make It
In a spice grinder or mortar, coarsely grind the fennel seeds. In a small skillet, combine the fennel seeds, olive oil and garlic. Cover and cook over low heat until the garlic is softened but not browned, about 4 minutes. Remove from the heat. Stir in the Pernod and set aside to cool.
Cut the stalks from the fennel bulbs; reserve the fennel bulbs for another use. Snip off all the feathery fronds and chop them coarsely. Quarter the stalks lengthwise and reserve.
Make three 1/2-inch-deep slashes across the fish on each side. Set the fish on a platter and rub it with the fennel oil, pushing the seeds into the slashes. Season the fish inside and out with salt and pepper and sprinkle with the lemon juice. Stuff the cavity with the lemon slices and all but 2 tablespoons of the chopped fennel fronds. Rub the remaining 2 tablespoons of fronds on the fish, pushing them into the slashes. Cover with plastic wrap and refrigerate for at least 30 minutes or for up to 4 hours.
Light a charcoal grill. Open a hinged fish grill and arrange half of the fennel stalks on one side. Set the fish on top, cover with the remaining stalks and close the grill. Cook the fish over a moderately hot fire for about 25 minutes, turning it every 5 minutes, until browned and just cooked through. Transfer to a platter.
Alternatively, preheat the oven to 500°. Make a bed of the fennel stalks on a large baking sheet and set the fish on top. Roast in the upper third of the oven for about 20 minutes, or until almost cooked through. Remove from the oven and preheat the broiler. Broil the fish for about 2 minutes, rotating the pan, until nicely browned.
With 2 forks, push away the top fins and carefully lift the fillets off the bones. Spoon some of the accumulated juices over the fish and serve at once.