Bring a large pot of water to a boil and add a generous amount of kosher salt. Italians salt their water to taste like the sea. Cook the rigatoni until al dente, about 12 to 14 minutes. Drain well. DO NOT RINSE.
Meanwhile, in a large sauté pan, heat the oil over moderate heat. Add the onion to the pan and cook for 3 minutes. Stir in the garlic and cook for 2 minutes with the onion. Add the frozen vegetables.
Slice the cooked Italian sausages lengthwise once and then each half again so you end up with 4 long strips. Gather and the cut crosswise so you end up with small bite-sized pieces.
Add the sausage into the pan and stir to heat up. Add the tomato sauce and let simmer for 10 to 15 minutes, seasoning with the basil and oregano and tasting for salt and pepper. You should have two burners working side by side which will finish at the same time.
Add a bit of sauce to the pot of rigatoni to coat the pasta. Then continue to add the sauce to the pasta ensuring the ratio of sauce and pasta is to your taste.
If you aren't using spicy sausage you may wish to add a sprinkle of crushed peppers to spice up the dish. Serve with the parmesan cheese.