Preheat oven to 400°F and lightly grease a 9x13 casserole dish.
Butterfly each chicken breast and pound to an even thickness of approximately 1 inch. Season both sides with salt, pepper, and half the minced garlic.
Spread the fresh spinach evenly across the bottom of the prepared casserole dish.
In a medium bowl, combine the ricotta cheese, shredded parmesan, Italian seasoning, crushed red pepper, and remaining minced garlic. Stir until smooth and well combined.
Place the seasoned chicken breasts on top of the spinach layer. Spread the ricotta mixture generously and evenly over each piece of chicken.
Pour the marinara sauce over the top, then sprinkle the extra parmesan cheese generously over everything.
Bake at 400°F for 30 minutes, or until the chicken reaches an internal temperature of 165°F. Let rest for 5 minutes before serving.