Combine first 5 ingredients in a small Dutch oven; bring to a boil. Reduce heat; simmer, uncovered, until mixture is reduced to 1 pint. Strain mixture through several layers of damp cheesecloth, discarding fish head, vegetables, and spices. Set fish stock aside.
Combine wine, tomatoes, lemon juice, fish stock, 1/2 teaspoon salt, 1/4 teaspoon pepper, and red pepper in skillet. Cook over medium heat 25 minutes or until mixture is reduced by half. Set aside; keep warm.
Combine minced parsley, thyme, garlic, bay leaves, remaining salt and pepper, and allspice in a small bowl; blend well. Rub herb mixture over surface of fillets; set aside.
Sauté chopped onion in olive oil in a large skillet until tender; set onion aside, reserving oil in skillet. Add fillets to skillet; top with onion. Cover; cook over medium heat 10 minutes.
Transfer fillets to a serving platter lined with toast points. Pour reserved sauce over fish, and garnish with lemon slices and fresh parsley sprigs. Serve immediately.