Crush the saltine crackers on a cutting board with a rolling pin
Add parmesan cheese and mix together with your hands
Heat the spinach in a microwave for a few minutes and cover the bottom of a baking dish (if it is too cold it will effect the baking time)
Place the fish on top of the spinach
Spread the mayonnaise over the fish so that it is evenly covered.
Cover with cracker and cheese mixture
Sprinkle a little paprika and dried parsley over the top of all (optional)
Cover baking dish with tin foil and bake for 45 minutes