Baking the cod on a wire rack allows the fish to get crisp on all sides.
Preheat oven to 400 degrees. Combine rice cereal, oil, parsley, zest, and salt.
Set a wire rack on a rimmed baking sheet. Press fish in crumb mixture, turning to coat. Transfer to wire rack. Bake until golden brown and cooked through, 14 to 16 minutes. Divide fish and spinach among 4 plates.
Squeeze lemon wedges over fish and spinach.