Preheat your oven to 350°F (175°C).
Gather all your ingredients in one place.
In a large bowl, combine the meatloaf mix with the diced red onion and celery. Add eggs, soy sauce, ketchup, oregano, parsley, garlic powder, and black pepper. Fold in quick oats and light brown sugar.
Transfer the meat mixture into a loaf pan or round Pyrex dish and shape it into a loaf.
Mix together the remaining ketchup with stone ground mustard and paprika. Brush this topping over the meatloaf.
Bake in the oven for 75-85 minutes until it reaches an internal temperature of 160°F (70°C).
Let the meatloaf rest for about 10-15 minutes before slicing.