Preheat oven to 350°F (177°C). Spray a 9X13 inch baking dish with nonstick cooking spray.
Cook pasta (16 ounces) according to package instructions, in a large pot, just until al dente. Drain and set aside. Dry out the pot and set it aside.
In another large pot, brown sausage (1 1/2 pounds) over medium heat, crumbling with a spoon as it cooks, until no longer pink; Remove sausage to a paper towel-lined plate; set aside.
Pour off and discard all but 2 tablespoons of the fat from the pan. Add the onion (2 cups) and garlic (1 tablespoon) then sauté on low heat until they're very soft about 10 minutes.
Turn up the heat to medium. Add the dried Italian seasoning (1 1/2 tablespoons), salt (1/2 teaspoon), and pepper (3/4 teaspoon) to the onion mixture and continue to sauté, stirring constantly, until fragrant, 1-2 minutes.
Add spaghetti sauce (1 jar), alfredo sauce (1 jar), and drained sausage, to skillet and mix.
In the dried pasta pot combine the drained pasta, half the mozzarella, and the sausage-sauce mixture. Mix until evenly combined. Pour into prepared baking pan. Evenly sprinkle top with remaining mozzarella. Bake, uncovered, in preheated oven for 40-50 minutes, until heated through and cheese is melted. Garnish with fresh parsley. Serve.