Sear the sliced sausage medallions in a large skillet or braiser over medium heat until browned and slightly crisp, approximately 4 minutes. Transfer the sausage to a paper towel-lined plate while reserving the rendered sausage oil in the skillet.
In the same skillet, sauté the mushrooms, yellow and red bell peppers, and minced garlic for about 3 minutes, or until the mushrooms develop a light brown color.
Add the pasta, diced fire-roasted tomatoes, chicken broth, and Cajun seasoning to the skillet. Stir to combine the ingredients evenly, then cover the skillet and bring the mixture to a boil.
Lower the heat to medium and simmer the pasta for 12–15 minutes, stirring every couple of minutes to prevent sticking. Cook until the pasta is tender and al dente.
Add chunks of cream cheese to the skillet, stirring continuously until it has melted into a rich, creamy sauce.
Return the cooked sausage to the skillet, stirring to coat it evenly in the sauce. Garnish with freshly chopped parsley and red pepper flakes, if desired. Serve immediately.