Preheat oven to 425°.
Sprinkle salmon fillets with salt and pepper. Place the fillets, skin sides up, in a large skillet or small roasting pan. Spoon chopped tomato around fillets, and drizzle fillets with soy sauce. Wrap handle of skillet with foil, and bake the fillets at 425° for 12 minutes or until fish flakes easily when tested with a fork. Remove skin from fillets, and discard skin. Remove fillets from pan, and keep warm. Add the chopped tarragon and mustard to tomato, stirring well. Spoon tomato mixture over fillets. Garnish with tarragon sprigs, if desired.