In a large pot, heat the olive oil over medium heat. Add the diced onion and sliced kielbasa. Cook for about 5 minutes, or until the onion is soft and the kielbasa is browned.
Stir in the minced garlic and cook for an additional minute until fragrant.
Add the elbow macaroni, chicken broth, smoked paprika, mustard powder, black pepper, and salt to the pot. Bring to a boil, then reduce the heat to low. Cover and simmer for 8-10 minutes, or until the pasta is cooked al dente.
Once the pasta is cooked, stir in the milk, shredded cheddar cheese, and grated Parmesan cheese. Mix until the cheese is melted and the sauce is creamy.
Remove from heat and let it sit for a couple of minutes to thicken. Garnish with chopped parsley before serving.