1. Bring a large pot of lightly salted water to boiling. Cook pasta according to package directions. Drain and set aside.
2. Meanwhile, add walnuts to a large nonstick saute pan over medium heat; toast 5 minutes, stirring occasionally. Remove to a cutting board to cool, then roughly chop.
3. In same pan, add chicken sausage. Cook over medium heat 5 to 7 minutes, breaking apart with a wooden spoon, until browned. Stir in flour; cook 1 minute. Add broth and bring to a simmer over medium-high heat. Mix in apples and cook 2 minutes. Stir in spinach until wilted. Mix in walnuts, Asiago, salt and pepper. Transfer to a bowl with pasta; stir to combine. Serve immediately.