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 for 5 to 7 minutes, stirring occasionally, until browned. Remove the sausage from the skillet and set aside.
In the same skillet, add the diced onion and green bell pepper. Sauté for 5 minutes until the vegetables are softened.
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. Season with salt and black pepper to taste.
Bring the sauce to a simmer and cook for 8 to 10 minutes, stirring occasionally, until slightly thickened.
Return the browned kalbasa sausage to the skillet and stir to combine with the sauce.
Add the cooked pasta to the skillet and toss everything together until the pasta is evenly coated with the sauce and sausage mixture.
Remove from heat and sprinkle grated Parmesan cheese and chopped fresh parsley over the top before serving.