Preheat oven to 350°. Cook noodles according to package directions.
Meanwhile, in a small bowl, combine sour cream, mayonnaise and lemon juice; set aside.
In a large saucepan, melt butter. Stir in flour until blended. Gradually stir in milk. Bring to a boil; cook and stir 2 minutes or until thickened. Reduce heat; stir in 1/3 cup cheese, stirring until melted. Remove from heat; stir in sour cream mixture. Add spinach, stuffing mix, bread crumbs and tuna.
Drain noodles and place in a 13x9-in. baking dish coated with cooking spray. Top with tuna mixture; sprinkle with remaining cheese.
Cover and bake 35 minutes. Uncover; bake 5-10 minutes longer or until lightly browned and heated through.