Bring a large pot of water to a boil and cook pasta according to the package instructions. Drain, rinse with cold water, and set aside. Meanwhile, sauté the onion in a large, non-stick skillet for about 4-5 minutes, until tender.

Add mushrooms and kielbasa to the onions and cook for about 5-7 minutes, until the mushrooms are cooked through.

Add heavy cream, pasta, dill, and some salt and parmesan cheese.  Mix, then taste if there is enough seasoning. Return the dish to the stove and cook for several more minutes, until the sauce has thickened.

Add mozzarella cheese to the top and serve immediately.