Preheat oven to 190 degrees C. Lightly coat a 20x30cm baking dish with cooking spray.
Melt butter in frying pan over medium heat. Add onion and saute for 1 minute. Stir in crab meat, parsley, garlic powder salt and pepper then cook 1 minute more. Remove from heat then stir in crushed crackers.
Spread mixture over fillets; sprinkle with lemon juice and Parmesan cheese. Roll up fillets, seal with toothpicks then place in prepared baking dish. Dot each roll with butter and cover dish tightly with foil.
Bake in preheated oven for 15 to 17 minutes until fish flakes.