Preheat oven to 350°. Cook manicotti shells according to package directions; drain. Meanwhile, in a small saucepan, melt butter. Stir in flour until smooth; gradually add milk. Bring to a boil; cook and stir until thickened, 2 minutes. Remove from the heat; stir in Parmesan cheese.
In a small bowl, combine the crab, ricotta cheese, mozzarella cheese, lemon-pepper seasoning, pepper and garlic powder. Stuff manicotti shells with crab mixture. Spread 1/4 cup sauce in an 8-in. square baking dish coated with cooking spray. Top with stuffed manicotti. Pour remaining sauce over top.
Bake, covered until heated through, 25-30 minutes. Just before serving, sprinkle with parsley and if desired, additional grated Parmesan cheese.