1. In a large dutch oven or soup pot over medium heat, melt the butter. Add the onions and cook until just starting to brown. Stir in garlic, Italian seasoning, salt, pepper, and red pepper flakes. Cook 1 minute.
2. Add chicken broth and stir well. Then add the uncooked chicken breasts and sun dried tomatoes.
3. Bring to a simmer and cover, reduce heat to medium-low and cook for 12-15 minutes, stirring occasionally, until chicken breasts are cooked through. The chicken needs to reach an internal temperature of at least 165°F (74°C).
4. Meanwhile, cook the pasta in boiling salted water to al dente, according to package directions.
5. When the chicken is cooked, remove from the soup and shred. In a separate bowl, whisk together cream and cornstarch.
Stir the shredded chicken, cooked pasta noodles, spinach, and the cream and cornstarch mixture back into the pot and heat through.
6. Serve with cheese as desired.