Begin by bringing a large pot of salted water to a rapid boil. Once boiling, add in the spaghetti and cook it according to the instructions on the package until it reaches an al dente texture. Drain the pasta and set it aside for later use.

While your spaghetti is cooking, heat up some vegetable oil in a separate pan over medium-high heat. Once heated, add in your shredded chicken and season it with a pinch of salt and pepper to amplify the flavor. Cook the chicken until all sides are a beautifully golden brown before removing it from the pan and setting it aside.

Using the same pan you cooked your chicken in, melt some butter over medium heat. As soon as the butter has fully melted, stir in the minced garlic and chopped bell peppers. Sautee them for about 3-4 minutes or until the peppers have reached a slightly softened consistency.

Now it’s time to create the delectable sauce that will tie all of these ingredients together! Add diced Velveeta, cream cheese, and white cheddar cheese to your pan with the peppers and garlic, stirring until all of the cheeses have melted together in delicious cohesion. Gradually pour in the chicken broth, heavy cream, and milk while continuously mixing to create a smooth consistency. Toss in your sliced baby bella mushrooms and stir everything up until they have become slightly softened as well. Let this sauce simmer for about 5 minutes to thicken it up.

As your sauce simmers, preheat your oven to 350°F (175°C). In a large casserole dish, combine your cooked spaghetti, chicken, and creamy sauce. Mix everything together until each ingredient is evenly coated. Finally, pop this dish into the oven for about 25-30 minutes, or until the top has reached a gorgeous golden brown and bubbly texture.

Once your chicken spaghetti is finished baking, allow it to cool for a few minutes before serving. For extra freshness and color, sprinkle some minced parsley on top as a garnish if desired.