Preheat your oven to 425°F.
In a large baking dish or oven-safe pan, whisk together the alfredo sauce, chicken broth, pesto, and red pepper flakes if using.
Stir in the shredded chicken, uncooked pasta, and diced tomato. Mix until everything is well coated.
Cover tightly with foil and bake for 30 to 40 minutes, or until the pasta is tender.
Remove from the oven and stir to ensure the pasta is fully cooked.
Stir in the fresh spinach, then sprinkle the shredded cheese evenly over the top. Return to the oven and broil uncovered for 1 to 2 minutes, just until the cheese is melted and bubbly.
Serve hot and enjoy! Great with garlic bread or a crisp side salad.