Put instant stuffing with seasoning in food processor and chop. Be sure not to blend to a powder as this is the substance that will hold the meatloaf together. If you do not have a food processor you can put stuffing mix directly with hamburger.
Add stuffing mix, hamburger, mustard, and eggs. Mix well.
Take half of the mixture and put into loaf pan.
Make a well in the middle of the hamburger mixture previously put into the loaf pan.
place string cheese in the well.
Add the rest of the meatloaf mixture in the pan. Then add topping (ketchup or barbecue sauce)
Cook at 350 for one hour.
Let meatloaf cool and set for 10 minutes. Cut and serve.