Saute the leeks and celery in the stock in a medium-size skillet over medium heat, until they are slightly tender.
Stir in the bread crumbs and dill and remove from heat.
Rub the fish inside and out with one half of the lemon.
Stuff the bread crumb mixture into the fish and close with metal skewers or sew closed.
Place on a shallow, rectangular baking dish coated with no-stick spray.
Wrap the tail of the fish with foil to prevent burning.
Squeeze the remaining lemon half over the fish.
Bake at 350° for about 40 to 45 minutes or until the fish flakes easily when tested with a fork.
Place the fish carefully on a serving platter.
Surround generously with parsley and scallions, if desired.
Place one of the cherry tomato halves over the fish eye.
Garnish with lemon slices.