Concentrated onion soup flavorfully incorporates the spicy bite of an onion and the savory flavorings like paprika, black pepper, and bullion that are in the soup mix.
Using onion soup allows you to avoid the fuss of gathering, measuring, and adding various seasonings. It's also super easy to incorporate into your meatloaf.
Fold the soup mix into the meat, add the other ingredients, form the meatloaf, and bake it. When it has 20 or 30 minutes left to bake, you can top it with a ketchup glaze.
Since seasoned bread crumbs are often heavily salted, consider using plain bread crumbs instead, and don't add more than one packet of soup unless you're doubling the recipe.