Heat olive oil in a large oven-safe skillet over medium-high heat. 

Add chicken breast fillets and cook for about 3 to 4 minutes per side until they’re golden brown and release easily from the pan. Remove chicken breasts from the pan and set aside.

In the same skillet add onion and cook for 3 minutes. 

Add garlic and cook for an additional 30 seconds. 

Add pasta, chicken broth, diced tomatoes and Italian seasoning.  

Bring the mixture to a boil and then reduce the heat to medium-low.  Cover and simmer for 15 minutes, stirring every 3 to 4 minutes to prevent the pasta from sticking to the bottom of the pan. 

Preheat oven to 400°F. Stir in spinach and return chicken to the skillet.  

Top the dish with mozzarella and Parmesan cheeses. 

Place dish in the oven and bake for about 10 to 15 minutes or until chicken reaches an internal temperature of 165°F and cheese is melted.