Preheat oven to 350F. Cook ziti in lightly salted boiling water according to pkg label; drain.
Heat oil in small skillet over med-high heat. Add sausage and cook for 10 min, turning frequently until browned. Remove from skillet.
Prepare sauce: Melt butter in a med saucepan; remove from heat. Add flour, 1 tsp salt and 1/2 tsp pepper. Gradually add milk, stirring until smooth. Over med-high heat, bring milk mixture to boiling, stirring constantly.
Remove sauce from heat and stir in 1/4 c Parmesan. Place drained ziti in large bowl; pour sauce over ziti and toss to combine.
Cut sausage into 1/2 inch thick slices. Set aside.
Make cheese filling: In medium bowl, mix ricotta with 1/4 cup Parmesan, egg, chopped parsley, 1/2 tsp salt and 1/8 tsp pepper; mix well. Spoon half of ziti mixture into a 2 1/2 quart baking dish.
Spread cheese filling on top of ziti mixture; spoon on remaining ziti. Arrange sliced sausage on top. Sprinkle casserole with mozzarella and paprika.
Place casserole on center rack of oven and bake uncovered for 30 minutes or until cheese is melted and casserole is bubbly. Let stand 5 min before serving.
Nutrition Info Per Serving: Calories 724 Total Fat 43 g Cholesterol 158 mg Sodium 1486 mg Potassium 508 mg Total Carbohydrate 51 g Dietary Fiber 5 g Sugars 5 g Protein 34 g