In a large bowl, stir together the ricotta, 1/2 cup of the parmesan, spinach, onion powder, garlic powder, and dried red chili flakes until well combined. Set aside.
Pour the marinara sauce into a baking dish. Set aside.
Place a large cutting board on your counter top. Place a sheet of parchment paper or plastic wrap on top of the cutting board. Lay one chicken thigh on the board and cover with another sheet of parchment or plastic wrap. Using a meat tenderizer or a rolling pin, firmly pound the chicken flat to 1/4 of an inch thick.
Once the chicken has been flattened, sprinkle with the salt and half the ground black pepper.
Evenly distribute the ricotta mixture onto the widest end of the flattened chicken thighs. Elongate the ricotta mixture and roll the chicken up to seal in the ricotta.
Place the rolled chicken seam side down into the marinara sauce.
Once all the chicken has been placed into the baking dish, top the chicken with the remaining ground black pepper and the remaining parmesan cheese.
Bake for 30 minutes. Remove from oven. Top with parsley and serve immediately.