Preheat your oven to 375°F (190°C).
In a large skillet over medium heat, combine the shredded chicken and marinara sauce. Heat until warmed through, then set aside.
In a mixing bowl, combine the almond flour, garlic powder, Italian seasoning, salt, and pepper.
In a separate bowl, whisk the eggs. Then, mix the egg mixture with the almond flour mixture until well combined.
In the prepared casserole dish, spread half of the almond flour mixture evenly across the bottom to form a crust.
Layer the warmed chicken and marinara sauce mixture over the crust, spreading it evenly.
Top the chicken with half of the shredded mozzarella and half of the grated Parmesan cheese.
Finish by topping the casserole with the remaining almond flour mixture, followed by the rest of the mozzarella and Parmesan cheese.
Bake in the preheated oven for 30 minutes, or until the cheese is bubbly and golden brown.
Once done, let the casserole cool for a few minutes before slicing. Garnish with fresh basil if desired.