Chop the onion and grate the carrot. Prepare the salad mix and slice the avocado.

In a bowl, mix ground meat, chopped onion, milk, breadcrumbs, salt, and pepper until well combined.

Divide the meat mixture into equal portions. Flatten each portion, place cheese in the center, and wrap the meat around to seal the cheese inside.

Heat salad oil in a pan over medium heat. Cook the patties until browned on both sides and fully cooked through.

In the same pan, combine ketchup, Worcestershire sauce, and butter to make the sauce. Simmer until slightly thickened.