1. Preheat oven to 375°F. Zest lemon (1 teaspoon), then juice (2 tablespoons). Crush crackers finely and place in large bowl. Coat 13- x 9-inch baking dish with spray, then spread both bags of rice mixture evenly in dish. Arrange fish in single layer over rice (wash hands) and sprinkle with seasoning, then spread cheese evenly over fish.
2. Place butter in large sauté pan on medium-high. Add onions; cook and stir 2 minutes. Stir in mushrooms and cook 3–4 minutes until mushrooms and onions are tender. Add spinach and cook 1 minute or until spinach is wilted. Remove from heat and let stand to cool slightly.
3. Add mushroom mixture, lemon zest, and lemon juice to bowl with crackers; toss to coat. Top fish with cracker mixture, adding any remaining cracker mixture around fish. Cover dish with foil; bake 15 minutes. Remove foil and bake 15–18 more minutes until centers of fillets flake easily and are 145°F. Serve.

Chef's Tip: Cooking the fish from frozen saves time and topping it with a creamy spread and moist breadcrumb mixture keeps it from drying out.