Preheat the oven to 400°F and line 2 baking sheets with parchment paper.
In a medium skillet over medium heat, heat the olive oil until shimmering. Add the onion and garlic and cook for 5 to 7 mins, until the onion is translucent and softened. Set aside to cool slightly.
Add the ground chicken, onion mixture, parmesan, ricotta, breadcrumbs, salt, pepper, egg, and parsley to a large mixing bowl. Mix until just combined, being careful not to over-mix.
Using a 3 Tbsp cookie scoop or your hands, form into meatballs that are about 2-inches in diameter, and place on the parchment-lined baking sheets with a little space in between each.
Bake for 25 mins, or until the internal temp reaches 165F and the meatballs are lightly golden. Optional: Broil each sheet pan for 2-3 mins at the end to get the tops of the meatballs extra golden brown.
Heat the marinara sauce in a large skillet or pot over medium-low heat, then add the meatballs. Serve topped with freshly grated parmesan and enjoy!
