Preheat oven to 400 F. Line a large rimmed baking sheet with aluminum foil, and spray the foil with nonstick cooking spray.
In a medium bowl, stir together the breadcrumbs, onion, parsley, Parmesan, salt, pepper, garlic, egg, and lemon zest until well combined. Add the ground chicken and use your hands to gently mix together with the other ingredients (don’t overmix). Using about ¼ cup of the mixture for each one (I used my ice cream scoop to keep them all the same size), form the meatballs by rolling the mixture into a ball with your hands. Arrange the meatballs on the prepared baking sheet.
Brush the top of each meatball with a little of the marinara sauce. Bake for about 14-15 minutes, or until the meatballs are golden brown and cooked through (they should register 165 F on an instant-read thermometer). When you take them out of the oven, brush the tops of the meatballs with a little more of the marinara sauce before serving.
To make ahead: Cook the meatballs then allow them to cool to room temperature. Place on a baking sheet and freeze until solid, then transfer to a resealable plastic bag. When ready to eat, defrost the meatballs in the refrigerator then reheat for 15 minutes in a 350 F oven.