Bring a large pot of salted water to a boil. Add the jumbo pasta shells and cook according to package instructions, MINUS 1-2 minutes (the shells will cook longer in the skillet so you don't want them to be too soft.) *Reserve 1 1/2 cups of pasta water, and then drain the pasta and place into a bowl. Lightly drizzle the cooked shells with a tablespoon of extra virgin olive oil, this helps the shells not to stick together. Set aside.

Using a large skillet over medium high heat, heat 1 tablespoon of olive oil. Add the sausage and cook, breaking up the sausage with a wooden spoon, until browned, cooked and no longer pink. Add the garlic; let cook for 1 minute. Reduce the heat to medium; add the crushed tomatoes, 2 tablespoons tomato paste, 1 cup of the reserved pasta water (just 1 cup; you will add more later if you need it) and 1/2 teaspoon salt. Stir together and let the sauce simmer for about 5 to 7 minutes, adding more cooking water if the sauce gets too thick. Taste the sauce and adjust any ingredients as needed.

Heat the remaining 1 tablespoon of olive oil in a separate skillet and cook the zucchini, mushrooms and spinach until softened for about 4 to 5 minutes. Season with salt and pepper. Remove from the heat and let cool for a few minutes. Add in the ricotta cheese and 1 tablespoon of the fresh diced parsley. Mix together until well combined.

Stuff 1 1/2 to 2 tablespoons of the mixture into each shell and then arrange them in the skillet with the sauce, seam-side up. Turn the heat back up to medium high, sprinkle on some freshly grated parmesan or mozzarella cheese and cover with a lid. Let cook for a few minutes, or until the shells are heated through and the cheese is melted. Sprinkle on remaining 1 tablespoon of diced parsley and serve immediately. Enjoy!