Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease it with cooking spray.
In a large mixing bowl, combine the ground chicken, breadcrumbs, Parmesan cheese, fresh parsley, egg, minced garlic, onion powder, oregano, salt, black pepper, and red pepper flakes (if using). Mix well until all ingredients are evenly incorporated.
Using your hands, form the mixture into meatballs about 1 to 1.5 inches in diameter and place them on the prepared baking sheet, leaving space between each meatball.
Drizzle a little olive oil over the meatballs to help them brown. Bake them in the preheated oven for 15-20 minutes, or until they are golden brown and cooked through (the internal temperature should be at least 165°F or 75°C).
While the meatballs are baking, warm the marinara sauce in a skillet over medium heat.
Once the meatballs are cooked, transfer them to the skillet with the warm marinara sauce and toss gently until coated.
Serve the chicken meatballs hot over pasta, in a sub sandwich, or as an appetizer with toothpicks.