Heat a large skillet to medium-high heat.
Add the olive oil and Italian sausage and cook for 3-4 minutes until the sausage is browned on all sides. Remove from the pan and set aside.
In the same pan, immediately add the red onions. Stir and sauté for 4-5 minutes until lightly caramelized.
Add the garlic and mini bell peppers, and sauté for 2-3 minutes. Season with a pinch of salt and pepper.
Stir in the crushed tomatoes and simmer for 8-10 minutes.
Bring a large pot of water to a boil. Add the pappardelle and cook stirring gently until al dente, about 11-13 minutes.
Drain the pasta and place in a large bowl.
Slice the Italian sausage into bite-sized pieces and add to the tomato sauce. Toss together the sauce, sausages, and pappardelle until combined.
Garnish with fresh basil and serve with shaved parmesan cheese.