In a large bowl, combine ground chicken, breadcrumbs, Parmesan cheese, parsley, red onion, garlic, oregano, salt, black pepper, and crushed red pepper flakes. Mix until well combined.
Form the mixture into meatballs, about 1 inch in diameter. Place the meatballs in the bottom of the crockpot.
Pour the marinara sauce over the meatballs, ensuring they are well coated.
In a separate bowl, mix the orzo and chicken broth. Pour this mixture over the meatballs and sauce in the crockpot.
Cover and cook on low for 4-5 hours or on high for 2-3 hours, until the meatballs are cooked through.
About 15 minutes before serving, stir in the heavy cream and feta cheese. Allow to heat through.
Serve hot, garnished with fresh basil.