Mince the onion and mix with olive oil in a microwave-safe container. Cover loosely with plastic wrap and microwave at 600W for 1 minute. Let cool.

In a bowl, combine breadcrumbs and milk. Add the cooled onion and remaining meat mixture ingredients. Mix until sticky and well combined.

Spread half of the meat mixture in a frying pan. Place pizza cheese in the center and cover with the remaining meat mixture, flattening it. Add vegetable oil around the edges and cook over medium heat for 3 minutes until browned. Cover and steam on low heat for 5 minutes.

Wipe off excess oil with a paper towel. Flip the patty onto a plate and return it to the pan. Cover and steam on low heat for 7–8 minutes until fully cooked.

In the same pan, add ketchup and Worcestershire sauce. Heat over medium until bubbling, then simmer for 1 minute. Add butter and stir until melted.