Preheat the oven to 375°F (190°C).
In a large mixing bowl, combine the ground beef, Parmesan cheese, almond flour, eggs, minced garlic, dried Italian herbs, salt, and black pepper. Mix until well combined.
Roll the mixture into small meatballs, about one inch in diameter, and set aside.
Heat a skillet over medium heat and add the meatballs in batches, browning them on all sides for about 5-7 minutes. Remove and place them in a baking dish.
In the same skillet, add the marinara sauce and heat it through. If using, stir in the red pepper flakes.
Pour the marinara sauce over the meatballs in the baking dish, ensuring they are well covered.
Top the casserole with shredded mozzarella cheese.
Cover the baking dish with aluminum foil and bake for 25 minutes. After that, remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Once cooked, remove from the oven and let it cool for a few minutes. Garnish with fresh basil if desired.