Preheat oven to 350 and spray loaf pans. You can use just the one bigger loaf pan. Or you can make a mini loaf, plus the larger loaf pan. Then you will have a mini loaf for a future lunch.
Place thawed ground beef in a large mixing bowl.
Mix together eggs and milk in a small mixing bowl and blend. Pour over ground beef.
Dice onion and add onion to beef mixture. Also add oats.
Add parsley, salt, and sage to ground beef. Mix ground beef, milk mixture, onion, oats, and spices all together with a fork.
Scoop meatloaf mixture into loaf pan (s). Pat into pan.
Place pans into oven and set the timer for 50 minutes.
While meatloaf (s) are cooking, mix together the ketchup, brown sugar, and mustard for the meatloaf glaze.
After 50 minutes, check the meatloafs. Pour out some, but not all of the extra juice in the pan.
Add the glaze and put the meatloaf back into the oven for another 10 minutes. The mini meatloaf will only need a few more minutes. Check for doneness with kitchen thermometer. It is done when temperature reaches 150 degrees.