Combine ground beef, condensed French onion soup, bread crumbs, oats, beaten egg, dried parsley, salt, and pepper in a bowl. Mix well. Pack into a loaf pan.
Bake in the preheated oven until no longer pink in the center, about 1 hour and 15 minutes. An instant-read thermometer inserted into the center should read at least 160 degrees F (70 degrees C). Let rest 5 minutes before cutting.