Preheat oven to 400ºF. In a large bowl, combine all meatball ingredients together (using your hands is the easiest way). Roll into lime-sized meatballs and place in a single layer on parchment-lined baking sheets. Bake until browned, about 20 minutes.
Meanwhile, heat oil in a heavy saucepan over medium heat. Add onion and a pinch of salt, then cook until very soft, about 12 minutes. Add garlic and ginger and cook a minute more, then add the ketchup, orange juice and brown sugar and bring sauce to a simmer.
Whisk cornstarch into soy sauce until smooth, then whisk into the sauce. Bring to a boil then reduce heat to simmer for 10 minutes, until thickened and glossy. Taste and season with more salt if desired.
Add meatballs and continue cooking until sauce is very thick and meatballs are cooked through to 165ºF, about 15 minutes more.