Preheat the oven to 350°F/177℃ with the rack in the middle. Pour about one tablespoon of oil into a small-medium saucepan, and heat it on medium.
Add the onions, garlic, and bell pepper, and saute for a minute or two to let the flavors bloom. Be careful not to let it burn. Then let it cool.
Place the beef, parsley, breadcrumbs, egg, thyme, white pepper, cayenne, Worcestershire sauce, and beef bouillon powder into a medium bowl. Add the cooled onion mixture, followed by the milk and salt. Mix lightly until everything has been thoroughly combined.
Form meatloaf into a loaf on a rimmed baking pan or place it in a 5×9-inch loaf pan, lightly press so that it’s evenly distributed in the pan.
Bake for about 40 minutes, then carefully remove from the oven.
Mix the ketchup, mustard, and brown sugar in a small bowl. Then brush the meatloaf with the ketchup glaze.
Return meatloaf to the oven. Continue baking for another 20 minutes or until an instant-read thermometer inserted into the center registers 160℉/72℃.
Let it stand for 10 minutes before slicing and serving.