Bring a large pot of salted water to a boil. Add the elbow macaroni and cook according to package instructions until al dente, about 8 to 10 minutes. Drain and set aside.
While the pasta cooks, heat olive oil in a large skillet over medium heat.
Add the sliced kalbasa sausage to the skillet and cook, stirring occasionally, until browned and heated through, about 5 minutes. Remove the sausage from the skillet and set aside.
In the same skillet, add the diced onion and green bell pepper. Sauté until softened, about 5 minutes.
Add the minced garlic and cook for 1 minute until fragrant.
Stir in the diced tomatoes with their juice, tomato sauce, dried Italian seasoning, and crushed red pepper flakes. Bring the mixture to a simmer and cook for 8 to 10 minutes, stirring occasionally, until the sauce thickens slightly.
Return the cooked kalbasa to the skillet and stir to combine. Season the sauce with salt and freshly ground black pepper to taste.
Add the cooked pasta to the skillet and toss everything together until the pasta is well coated with the sauce.
Sprinkle the shredded mozzarella and grated Parmesan cheese evenly over the pasta. Cover the skillet with a lid and cook for 2 to 3 minutes, or until the cheese melts.
Remove from heat and garnish with chopped fresh parsley before serving.