In a large pot of salted boiling water, cook the penne pasta until al dente, according to package instructions. Drain and set aside.
In a large skillet over medium heat, remove the casing from the Italian sausage and crumble the meat into the skillet. Cook until browned and fully cooked, about 6-8 minutes.
Add the chopped spinach to the skillet and cook until wilted, about 2 minutes.
In a large mixing bowl, combine the cooked penne, sautéed sausage and spinach, ricotta cheese, marinara sauce, garlic powder, onion powder, and red pepper flakes (if using). Mix well until everything is evenly incorporated.
Season with salt and pepper to taste.
Transfer the mixture into a greased 9x13 inch baking dish. Top with shredded mozzarella cheese and grated Parmesan cheese evenly over the top.
Bake in the preheated oven for 25-30 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let it sit for 5 minutes before serving. Garnish with fresh basil leaves.
Notes
Let the dish sit for a few minutes before serving for better slicing.