Preheat the oven to 375°F. Grease a 9-inch loaf pan with cooking spray or butter.
Add the olive oil to a medium skillet over medium-low heat. Add the onions and garlic and cook, stirring, until the onions are translucent, about 3 minutes. Transfer the onion mixture to a large bowl and let cool completely.
While the onions cool, in a small bowl stir together the breadcrumbs and milk. Let sit for 5 minutes.
Add the breadcrumbs mixture to the bowl with the onions then add the ground chicken, eggs and Parmesan cheese. Using your hands, work together the mixture until it is well-combined.
Transfer the meat mixture to the prepared pan.
Bake the meatloaf for 45 minutes then remove it from the oven and top it with the ketchup. Return the meatloaf to the oven and continue baking it until it reaches an internal temperature of 165°F, about 15 more minutes.
Remove the meatloaf from the oven and let it cool for 10 minutes in the pan before slicing and serving.