Preheat your oven to 350° degrees.
Butter an 8-inch-square baking pan.
Pat down the fish with a paper towel and sprinkle salt on each side.
Cook crab in a pot for about 10 minutes or until fully cooked, peel and place in a small bowl.
Chop a small onion, and use 2 tablespoons of the butter to sauté onion in a pan on medium heat.
Take about 2 cups of crackers and place them in the food processor until all crumbled up. Then mix them with the onion.
Once the pan has cooled, combine 1 ½ cups of crackers with the crabmeat, mayonnaise, parsley, and lemon juice,
Divide stuffing into 2 piles, lay the fish fillet, dark side up, on a work surface, and spoon crabmeat mixture into the center of the fish. Roll the ends up around the filling.
Place the fish, seam side down, and lay it into the baking pan.
Brush melted butter on top, then sprinkle fillets with crackers and parsley.
Bake until the fish is opaque and cooked through, 20 to 25 minutes.