Boil pasta in a large pot of salted water per the package instructions just until al dente. Drain well, then set aside.
Preheat oven to 375°F. Prepare a 13x9-inch baking dish with non-stick cooking spray. Set aside.
Add sausage and onion to a large deep skillet or pot. Cook the sausage over medium-high heat until no pink remains. (If you use a large pot it can double as a mixing bowl.)
Add minced garlic, Italian seasoning, salt and pepper, cooking for 1-2 minutes longer. Drain excess grease from pan.
To the sausage mixture add the marinara sauce, tomato sauce and tomato paste. Simmer on medium heat and stir just until the tomato paste has completely dissolved, then remove the pot from the heat.
Add cooked pasta to the sauce mixture and stir until fully coated.
To a separate medium mixing bowl add the cottage cheese, ricotta, 1 ½ cups mozzarella cheese and 1/4 cup Parmesan cheese. Mix with a large spoon or rubber spatula until fully combined.
Pour half of pasta mixture into the prepared baking dish. Spread with entire cottage cheese-ricotta mixture.
Pour remaining pasta mixture on top of the cottage cheese. Top with remaining mozzarella, and 1/4 cup Parmesan cheese.
Transfer dish to the oven and bake uncovered for 35-40 minutes or until bubbly around the edges and the cheese is lightly golden brown.
Garnish with fresh parsley, slice and serve.