Cook the spaghetti according to the package directions. Drain well before adding to the sauce.
While the pasta is cooking, cook the ground sausage in a large skillet until no longer pink. Add the taco seasoning and water and stir to combine. Stir in the marinara sauce, add the spaghetti, and toss to coat.
Stuff the shells with the spaghetti and top with tomatoes, Mexican cheese, a sprinkle of parmesan, and parsley.
Serve immediately.
