Step 1: Bring a large pot of salted water to a boil and cook the pasta according to package directions until al dente. Reserve 1 cup of pasta water before draining.
Step 2: While pasta cooks, heat olive oil in a large skillet over medium-high heat. Add the sliced smoked sausage and cook for 3-5 minutes per side until well-browned. Remove sausage from the pan and set aside.
Step 3: In the same skillet, add the diced onion and bell pepper. Sauté for 5 minutes until softened. Add the garlic and red pepper flakes, cooking for another 60 seconds until fragrant.
Step 4: Pour in the heavy cream and bring to a simmer. Use a wooden spoon to scrape the browned bits from the bottom of the pan. Let the sauce simmer for 3-4 minutes until slightly thickened.
Step 5: Stir in the Parmesan cheese until melted and smooth. Return the sausage and the cooked pasta to the skillet.
Step 6: Toss everything together to coat. If the sauce is too thick, add reserved pasta water one tablespoon at a time until the desired consistency is reached. Season with salt and pepper.
Step 7: Garnish with fresh parsley and serve immediately while hot.