Preheat your oven to 400 degrees F and line a rimmed baking sheet with parchment paper. In a large mixing bowl, combine the ground chicken, breadcrumbs, Parmesan, beaten egg, garlic, parsley, Italian seasoning, salt, pepper, and red pepper flakes if using. Use your hands to mix gently until everything is just combined. Do not overwork the mixture or the meatballs will be dense. The mixture will feel sticky, and that is normal with ground chicken.

Wet your hands with cool water before shaping each meatball. This keeps the mixture from sticking to your palms and helps you get a smooth, round shape. Scoop and roll the mixture into balls about 1 1/2 inches wide. You should get roughly 20 to 22 meatballs. Place them on the prepared baking sheet with a little space between each one.

Lightly brush the tops of the meatballs with olive oil. This encourages a little color on the outside even without frying. Bake for 18 to 20 minutes, until the outsides are set and lightly golden and an instant-read thermometer inserted into the center of one meatball reads 165 degrees F. They will look slightly firm and the bottoms will have a pale golden color on the parchment.

While the meatballs bake, pour the marinara sauce into a large saucepan or Dutch oven and warm it over medium-low heat, stirring occasionally. Keep it at a gentle simmer, not a rolling boil, so it does not scorch on the bottom.

When the meatballs come out of the oven, use a spatula or spoon to transfer them directly into the simmering marinara. Stir gently so each meatball gets coated in sauce. Let them simmer together for 5 to 8 minutes. This finishing step is important because it marries the flavors and keeps the meatballs moist all the way through.

Serve the meatballs and sauce over cooked spaghetti, creamy polenta, or zucchini noodles. Finish with freshly grated Parmesan and torn basil leaves. Set the extra sauce from the pan on the table because everyone always wants more.