Cook pasta according to package directions. Meanwhile, in a small saucepan, combine flour and milk until smooth. Bring to a boil; cook and stir for 2 minutes or until thickened. Remove from the heat; set aside.
In a large nonstick skillet, saute the mushrooms, onion and green pepper in oil until tender. Reduce heat; add the ham, 1/2 cup Swiss cheese and Parmesan cheese. Cook and stir until cheese is melted. Remove from the heat. Stir in 1/2 cup of the reserved sauce.
Drain pasta; stuff each shell with about 3 tablespoons of filing. Place in a 13-in. x 9-in. baking dish coated with cooking spray. Top with remaining sauce. Cover and bake at 350° for 30 minutes or until heated through. Sprinkle with parsley, paprika and remaining Swiss cheese. Yield: 8 servings.