Preheat oven to 400 degrees Fahrenheit and spray a large sheet pan with cooking spray.
Saute onion in butter in small saucepan until translucent.
Add ¼ cup of ketchup to the butter and onion. Let the ketchup get warm and remove pan from heat and let it cool.
While the ketchup cools, in a large mixing bowl combine 1 lb of ground beef, 1 egg, ¼ tsp garlic powder, ½ tsp sea salt, ½ tsp black pepper, ½ tsp mustard powder, ½ cup seasoned panko together. Mix until combined. Add cooled ketchup mixture and mix until thoroughly combined. It's okay if ketchup is slightly warm, but you don't want it hot.
Divide mixture into four small individual loaves on the sheet pan and add to oven.
While the meatloaf cooks, mix together the glaze by mixing ½ cup ketchup, ½ brown sugar and 1½ tsp ground mustard.
After 20 minutes of baking, remove meatloaf and evenly divide glaze on the top of each meatloaf. Return meatloaf to oven and finish cooking until internal temperature is 165 degrees.