For the Pasta:

1. Bring a large pan of salted water to a boil. Add the pasta and cook until al dente. Drain and toss with butter.

For the Chicken and Sauce:

1. Optional: For quicker, more even cooking, slightly flatten breasts with a kitchen mallet. If they are very thick, slice them in half horizontally before flattening. 
2. Season with salt and pepper.
3. Heat a skillet over high heat. When pan is hot, add 1 tablespoon oil.
4. When oil is hot, put chicken breasts in pan and cook until golden brown on both sides and cooked through. Remove chicken from pan.
5. Let chicken cool for a few minutes, then slice. Set aside.
6. Add remaining tablespoon oil to pan. Add onions and cook until softened.
7. Add red bell pepper and cook until almost softened.
8. Add the garlic, sundried tomatoes, and Italian seasoning. Stir, and cook for about 1 minute.
9. Deglaze pan with broth, scraping bottom to release any bits sticking to the bottom of the pan.
10. Add cream and bring to a simmer. Allow to simmer for 2 minutes. Add parmesan and cook until melted.
11. When cheese is melted turn off the heat and stir in baby spinach.
12. Salt and pepper to taste.
13. Combine pasta, chicken, and sauce.
14. Serve.