Melt the butter in a large stockpot. Add onions and chicken. Sauté, stirring occasionally until the onions are starting to soften.
Stir in the garlic, tomato paste, and sun-dried tomatoes for one minute.
Stir in chicken stock, half & half, and all the seasonings. Allow to simmer, stirring occasionally, for about 12 minutes.
Add pasta and reduce heat to medium-low; cook: stirring occasionally, until pasta is just cooked, about 12 minutes.
Reduce heat to low, and add spinach and cream cheese. Cook and stir until the cream cheese is completely melted and the spinach is wilted, 3-5 minutes.