Preheat oven to 175 degrees Celsius.
In a large bowl, combine ground beef, ground pork, breadcrumbs, milk, egg, salt, pepper, and onion powder until just incorporated.
On a sheet of parchment paper, flatten the meat mixture into a uniform rectangle approximately 2cm thick.
Distribute the shredded chicken and mozzarella cheese evenly across the center of the meat, leaving a 2cm border at the edges.
Using the parchment paper as a guide, roll the meat tightly into a loaf shape and seal the ends firmly to prevent leakage.
Place the loaf in a baking pan and bake for 55 minutes or until the internal temperature reaches 71 degrees Celsius.
Allow the loaf to rest for 10 minutes to stabilize the molten cheese and juices before slicing.