Add olive oil and sausage to a soup pot over medium-high heat. Brown the sausages for 5 minutes. If your sausages are particularly fatty, drain most of the grease off (I skipped this step since my sausages were fairly lean).
Add the mushrooms and sauté for another 3 minutes or so.
Stir in the garlic, Dijon mustard, sun-dried tomatoes, and red pepper. Cook for 2 minutes.
Add in the chicken broth, half-and-half, Cajun seasoning, and penne. Increase the heat to high. Once it reaches a boil, turn the heat down to medium (or medium-low if it continues to bubble a lot). Cook until the pasta is done and the sauce is reduced to your liking (about 20 minutes), stirring often so the pasta doesn't stick to the bottom of the pan.
Season with salt & pepper and stir in the basil. Top with freshly grated parmesan cheese if desired.