Open the sauce and place in 2 quart pot. Cook to a boil then turn down to simmer for about 1 hour: add spices of your choosing to taste! About 1/2 hour into the simmering of the sauce, open and place the rings of the kielbasa in the sauce.
Immediately start to boil your spaghetti in a quart pan of boiling water. After the spaghetti is cooked, drain and rinse with cool water. Place spaghetti in a large baking pan in the center of the pan.
Next, check to see if the kielbasa has swollen in the tomato sauce. If it has, take out of the sauce and place around the spaghetti in the baking pan. Next, slit the kielbasa carefully 1/2 way through in the middle around the whole kielbasa. Take your mozzarella cheese and place the cheese in the slits of the kielbasa. Pack it in slits carefully. Save a small amount available on the side. Next, take your sauce from the pan and pour over the kielbasa and spaghetti in the roasting pan and sprinkle remaining mozzarella cheese over the top of kielbasa and spaghetti.
Place baking pan in oven on 375°F and bake for about 15 to 20 minutes.