Preheat large Dutch oven or heavy bottom pot on medium heat and swirl oil to coat.
Add chicken and sprinkle with ¼ teaspoon salt and ¼ teaspoon ground black pepper. Sear for 3-4 minutes per side.
Add broth, pasta, bell pepper, Italian seasoning and remaining ¼ teaspoon salt and ¼ teaspoon ground black pepper. Gently stir, cover and bring to a boil.
Reduce heat to medium and cook for 10 minutes, stirring once after 2 minutes to prevent pasta from sticking.
Remove chicken onto a plate or cutting board.
In a large measuring cup whisk cold milk with cornstarch and pour over pasta. Stir gently, bring to a boil and simmer for a minute until sauce thickens a bit.
Turn off heat and add sun dried tomatoes, Parmesan cheese, spinach and garlic. Cover for a few minutes to let flavors develop.
Meanwhile, slice chicken into thin pieces.
Add chicken back to the pot, stir gently and serve immediately.
