Preheat your oven to 375 degrees Fahrenheit. Spray a 9 by 13 inch baking dish with cooking spray. Set aside.
Place a large pot of water over high heat to boil the penne. Once the water is at a roaring boil, season it with salt and add the noodles. Boil the noodles for 2 minutes less than the time stated on the box. Drain the pasta and set aside.
16 ounces penne, 1 teaspoon kosher salt
While the pasta is boiling, place a large skillet over medium-high heat. Heat the olive oil for 30 seconds before adding the onion, carrots, zucchini, red pepper, garlic, salt, and red pepper flakes. Sauté for 2 minutes. Add in the mushrooms. Cook until everything is soft and tender, about 3 to 4 minutes. Drain any excess liquid from the pan.
2 tablespoons olive oil, 1 medium yellow onion, 2 medium carrots, 1 medium zucchini, 2 garlic cloves, 1/4 to 1/2 teaspoon crushed red pepper flakes, 8 ounces sliced mushrooms, 1 teaspoon kosher salt
Add the diced tomatoes and tomato sauce, stirring to combine. Stir in the basil and oregano. Bring the sauce to a boil and then reduce to a simmer. Simmer for 5 minutes, stirring occasionally.
28 ounces diced tomatoes, 1/2 tablespoon dried oregano, 1/2 tablespoon dried basil, 8 ounces tomato sauce
Add the spinach to the sauce, allowing it to wilt.
3 cups baby spinach
In the casserole dish, combine the noodles and the sauce. Stir in 1 cup of the shredded mozzarella. Then stir in a second cup. Stirring it in 2 groups will prevent it from melting too quickly and allow it to be evenly distributed throughout the casserole. (Alternatively, combine all of this in the skillet if it is oven-proof.)
4 cups mozzarella cheese
Add the remaining 2 cups of mozzarella and the parmesan in an even layer over the top. Bake uncovered for 20 to 25 minutes or until the cheese on top is bubbly and beginning to brown. Serve warm and enjoy!
1/2 cup parmesan cheese