Use a sharp knife to cut the chicken into cubes. Then, in a large pot, melt the butter and brown the cubes of chicken on all sides over medium-high heat, 5-8 minutes.
Add the garlic and sauté with the chicken for 2 minutes, then add the pasta and chicken stock. Bring to a simmer, then cover and cook over low heat for 8 minutes. Stir occasionally to make sure the pasta doesn’t stick to the bottom.
Add the milk, cream cheese, pesto, sun-dried tomatoes, half the Parmesan, salt, and pepper. Give it a good stir to incorporate the cream cheese, then cover and simmer 5 minutes more.
When the sauce has thickened and the pasta is cooked to your liking, sprinkle on the rest of the Parmesan and serve.