Cook the spaghetti in accordance with the instructions on the packaging. Prep your vegetables and chicken while the spaghetti cooks.
Place a large pot or Dutch oven on medium-high heat with 1 teaspoon of olive oil. Add the chicken cubes and season with 1 teaspoon of Italian Seasoning, salt, and pepper to taste. Cook for 5-6 minutes until fully cooked through on both sides. Remove the chicken and set it aside.
Add an additional teaspoon of olive oil (if necessary, your pot may be well coated from cooking the chicken) along with the green peppers, red peppers, and onions to the pot. Saute until the veggies are translucent and fragrant.
Remove the vegetables and set them aside.
Reduce the heat on the stove to medium and add the butter. Once melted add the garlic.
Cook for 2 minutes and then add a few tablespoons of the broth to the pot. Deglaze the pan by using use a wooden or silicone spoon to scrape up any brown bits at the bottom of the pot. The brown bits have flavor and stay in the pot.
Add in the remaining broth, cream cheese, heavy cream, cheddar, Parmesan, fire-roasted tomatoes, 1 teaspoon of Italian Seasoning, salt, and pepper to taste.
Stir constantly and cook until the cheese melts. Taste the sauce repeatedly to ensure it meets your liking. Add additional Italian Seasoning, salt, or pepper as needed.
Add the cooked pasta, chicken, and vegetables back to the pot. Stir.
Reduce the heat to low and place the lid on the pot. Simmer for 15-20 minutes or until the sauce and pasta are well incorporated.