Preheat oven to 325°F. Line sheet trays with pan liners.
Mince garlic. Heat oil over medium heat in a tilt skillet or large sauté pan (depending on batch size).
Add onions and garlic. Sauté, stirring frequently, until onions are tender. Do not allow garlic to burn.
Use a large mixing bowl that will accommodate all of the beef. Alternately, you may make the recipe in batches. Note: You may use the bowl of a large stand mixer for this step.
Fold panko bread crumbs into wet ingredients and use hands to fold together.
Use gloved hands to work bread crumb mixture into ground beef. Ensure the bread crumb mixture is completely and evenly mixed into the beef. Note: You may also use a large stand mixer with paddle attachment for this step. Blend on low speed until combined.
Use a 1/2 cup scoop to portion meatballs onto tray: 5 across and 6 down (30 per tray).
Bake meatballs for 10-15 minutes until cooked to approximately 140°F.
CCP: Do not serve. See next step.
Make the glaze: Whisk ketchup and katsu sauce together in a mixing bowl.
After meatballs have reached approximately 140°F, spoon 1 Tbsp of glaze on top of each meatball.
Return meatballs to oven and finish cooking to a minimum internal temperature of 165°F for 15 seconds.
Transfer to a serving pan, cover, and hold hot for serving.