Combine ground beef and lamb with grated onion. Add egg, bread crumbs, salt, pepper and cumin and mix well. Cover and refrigerate for 30 minutes.
Shape mixture into 2 inch balls. Press 1 cheese cube into centre of each ball, sealing it inside. Heat the olive oil in a cast iron skillet and cook meatballs for about 10 minutes turning them occasionally.
For the honey mustard sauce
In a medium saucepan over medium heat, mix the honey, tabasco, both mustards and stir. Bring to a gentle boil. Reduce heat and simmer for 3 minutes, until a glossy sauce is formed. Set aside to cool.
Serve meatballs with honey mustard on the side for dipping.