Preheat oven to 375 degrees F (190 degrees C). Lightly coat a 9x13 inch baking pan with cooking spray.
Melt butter in frying pan over medium heat. Add onion and saute for 1 minute. Stir in crabmeat, parsley, garlic powder salt and pepper and cook 1 minute more. Remove from heat and stir in crushed crackers.
Spread mixture over filets; sprinkle with lemon juice and Parmesan cheese. Roll up filets, seal with toothpicks and place in prepared baking dish. Dot each roll with butter and cover pan tightly with foil.
Bake in preheated oven for 15 to 17 minutes until fish flakes.