1. Preheat oven to 400°.
2. Combine stock and mustard in a medium saucepan; bring to a boil. Gradually add polenta, stirring constantly with a whisk. Reduce heat to low, and cook 20 minutes, stirring frequently. Stir in Parmesan cheese, oregano, and 1/4 teaspoon salt.
3. Place panko and next 4 ingredients (through pepper) in a large skillet; cook over medium heat 3 minutes or until toasted, stirring frequently. Place panko mixture in a shallow dish. Combine 2 tablespoons water and egg in a shallow dish. Place flour in a shallow dish. Sprinkle fish with remaining 1/4 teaspoon salt. Dredge fish in flour; dip in egg mixture. Place fish in panko mixture, turning to coat.
4. Arrange fish on a baking sheet coated with cooking spray. Bake at 400° for 15 minutes or until done. Serve with lemon wedges and polenta.