1. Prepare pasta according to package directions; drain. Set aside. Prepare beef pot roast according to package directions. Remove beef from gravy or au jus; reserve gravy for another use. Shred beef with 2 forks. Keep warm; set aside.
2. Meanwhile, heat oil in large nonstick skillet over medium heat until hot. Carefully whisk in flour; cook 3 to 5 minutes or until lightly browned, whisking constantly. Whisk in milk; cook 8 to 10 minutes or until thick, whisking constantly. Remove pan from heat and stir in Monterey Jack cheese, salt and pepper, stirring until cheese is melted. Stir in pasta, 1/2 cup Gorgonzola cheese and sage.
3. Evenly divide pasta mixture among four plates; top with beef and sprinkle with remaining Gorgonzola cheese. Serve immediately.