Preheat oven to 350 degrees F (175 degrees C). Lightly grease a baking dish.
Mix ground beef, rice, parsley, egg, Worcestershire sauce, garlic powder, onion powder, and 1/4 teaspoon salt together in a bowl; form into 4 oblong mini-loaves. Season the outside of each loaf generously with pepper. Arrange loaves in the prepared baking dish.
Bake in the preheated oven until no longer pink in the center, 35 to 45 minutes. An instant-read thermometer inserted into the center of each loaf should read at least 160 degrees F (70 degrees C).
Heat olive oil in a skillet over low heat; saute onion in oil until soft and golden brown, 15 to 20 minutes. Season onion with 1 pinch salt; serve over meat loaves.