Cook the penne pasta in a large pot of salted boiling water according to package instructions until al dente. Drain and set aside.
In a large skillet over medium heat, add olive oil and minced garlic. Sauté for about 2 minutes until fragrant, but do not let it brown.
Add the red pepper flakes (if using) and chopped spinach to the skillet. Cook for an additional 2-3 minutes or until the spinach wilts.
In a large mixing bowl, combine the cooked pasta, ricotta cheese, 1 cup of Parmesan cheese, and marinara sauce. Stir in the garlic and spinach mixture along with Italian seasoning, salt, and pepper. Mix until everything is evenly combined.
Transfer the pasta mixture to a greased 9x13 inch baking dish. Top with the remaining Parmesan cheese and sprinkle the mozzarella cheese evenly over the top.
Cover the baking dish with aluminum foil and bake for 20 minutes.
Remove the foil and continue baking for an additional 10-15 minutes or until the cheese is bubbly and golden.
Once done, remove from the oven and let it cool for a few minutes before serving.
Garnish with fresh chopped parsley before serving.
Notes
Feel free to adjust the amount of red pepper flakes to your spice preference.