Preheat oven to 300ºF.

In a medium bowl, mix the ground meats, oats, egg, and milk together until well combined. Mold the mixture into balls about the size of a walnut, and arrange in a single layer in a Lodge 12-inch cast iron skillet. Bake for 45 minutes. Carefully drain any fat from the skillet.

Combine the remaining ingredients in a Lodge Chef Skillet, and cook over medium heat, stirring constantly, until the brown sugar, flour, and mustard are dissolved and the sauce is slightly thickened. Pour the sauce over the ham balls and bake another 20 minutes, basting occasionally.