Coat 9-inch pie plate with nonstick vegetable cooking spray.
Crumble saltines into egg whites in bowl; stir with fork. Let saltines soften, about 5 minutes. Stir in mayonnaise, onion, pepper seasoning and crab. Form into 4 equal-size patties. Place in prepared pie plate.
Bake in preheated 400 degree F oven 12 minutes, turning once.
Combine sour cream, horseradish and lemon juice.
Place patty on bun with lettuce and tomato; top with sauce. Makes 4 servings.