Thaw fish, if frozen; rinse and pat dry with paper towels. Set aside. For stuffing, thaw spinach; drain well, pressing out excess liquid. In a medium mixing bowl combine spinach, egg, croutons, Parmesan, sour cream, water chestnuts, and onion powder.
Place 2 fillets lengthwise in a 13 x 9 x 2-inch baking dish. Spoon one-fourth of the stuffing over each fillet in the dish. Fold fillets over stuffing. Repeat with remaining fillets and stuffing. Bake, covered in a 350 degree F oven for 30 to 35 minutes or until fish flakes easily with a fork.
Meanwhile, cook shrimp, if desired. In a 1-quart saucepan bring 1-1/2 cups lightly salted water to boiling. Add shrimp; return to boiling. Reduce heat simmer, uncovered, for 1 to 2 minutes or until shrimp turn pink. Drain. Cool slightly, then peel, leaving tail intact. Keep warm.
Prepare Quick Hollandaise Sauce. Transfer fish to a serving platter. Spoon some sauce over fish. Place 1 shrimp atop each fillet; garnish with dill, if desired. Pass remaining sauce. Makes 4 servings.
Quick Hollandaise Sauce
Place egg yolks in a blender container. Cover and blend about 5 seconds or until mixed. In a small saucepan heat butter or margarine, lemon peel, lemon juice, and a dash white pepper until butter is melted and almost boiling. With blender running at high speed and lid ajar, slowly pour in butter mixture. Blend about 30 seconds or until thick and fluffy. Serve immediately. (To reheat, place sauce in a small saucepan over very low heat. Heat, stirring constantly, until warm. If sauce is too thick, stir in 1 teaspoon to 1 tablespoon water.) Makes 2/3 cup.