Have fish cleaned but leave tail and head intact. Wash the fish well and pat it dry with paper towels.

Preheat oven to moderate (350°F.).

Heat the butter and in it cook the onion until it is wilted. Combine with the celery, bread crumbs, parsley, thyme, sesame seeds, half of the salt and half of the pepper.

Sprinkle the inside of the fish with the remaining salt and pepper. Spoon the filling into the cavity of the fish and skewer the opening. Place the fish in a baking dish and cover with the bacon slices.

Bake for forty-five minutes to one hour, or until fish flakes easily when tested with a fork. Garnish the fish with lemon slices and parsley, and serve.