1 Preheat oven to 350° F. 2 Lightly spray a 9-inch square casserole dish or baking pan with vegetable oil spray. 3 In a small saucepan, melt the margarine over medium-high heat. Cook the onion 2 to 3 minutes. 4 Transfer the onion to a medium bowl. Stir in the crabmeat, mustard, and Worcestershire sauce. Slowly fold in the beaten egg whites. Pour the mixture into the casserole dish. 5 Sprinkle the mixture with the cheese. 6 Bake for 25 minutes, or until lightly browned. Remove from the oven and cut into rectangles. Serve immediately.