Preheat oven to 425 degrees. Lightly spray a 13" X 9" baking dish with cooking spray.
Stir all sauce ingredients together in a medium size saucepan and bring to a boil. Keep a close eye on it as it begins to simmer because like any sugary sauce it will boil up and over the edge before you know it. Reduce heat and vigorously simmer until reduced by about a third.
Crack the eggs into a large mixing bowl and lightly beat with a fork. Add in the oats and milk and stir the mixture up.
Cut up leftover baked ham (usually from a whole bone-in ham) into small to medium pieces and pulse in small batches in a food processor until minced fine or ground up. Add to bowl.
Add the ground pork and mix WELL with your hands. Squeeze the mixture between your fingers. Don't be afraid to "over mix" because you want this loaf to be dense. Smash the mix firmly into the bottom of the bowl. Press down firmly with your open palm to compress the mixture.
At this point you decide how you need to divide these loaves up. I have small hands so I like to do thirds. But, if you are cooking for one, divide it into fourths and freeze after baking. Don't forget to adjust total baking time down a little for the smaller loaf size.
Place loaves in prepared baking dish and place on middle rack in the preheated oven. After 30 minutes, turn temperature down to 350 degrees, slide the rack out and VERY CAREFULLY gently pour or spoon simmering sauce over all the loaves. Continue to bake and baste for 1 1/2 hours (internal temperature should be checked after 1 hour attaining 160 degrees)
Please don't skip this next step. It will really make a difference in the end. The sauce will be thicker and the difference the basting makes on the loaf surface will be greatly appreciated when eaten as a cold sandwich.
**Using a baster, drizzle the sweet and sour sauce over entire surface of loaf every FIFTEEN MINUTES**
Once 160 degrees is reached, turn the oven off but don't open it. Let the loaves rest in the oven for at least 15 minutes. Baste one final time then using a spatula remove a loaf to a cutting board. Cut into slices as you would with any meatloaf, using light pressure and a sawing motion with a serrated knife (like a steak knife).
I will often double the sauce recipe. That way there is no doubt as to whether or not there will be enough sauce leftover to freeze in a zip lock freezer bag with the extra ham loaf.