Special equipment: 4-inch round biscuit cutter, or tuna or other can, top and bottom removed
Preheat the oven to 425 degrees F. Line a baking sheet with parchment paper or foil.
Break the meatloaf mixture into a large bowl and use your hands to lightly work in the onion, bread crumbs, egg, parsley, Worcestershire sauce, mustard, salt, Italian seasoning, garlic powder, and pepper until evenly mixed. Take care not to overwork the mixture.
Space the pancetta slices, if using, a few inches apart on the prepared pan and put the cutter on top of 1 piece. Divide the meatloaf mixture into 4 equal portions. Press a piece of cheese into the center and then press the meat around it to enclose it completely. Put a portion in the cutter and press gently so that it covers the pancetta evenly, and makes a neat, flat disk. Repeat with the remaining meatloaf mix to make 4 little loaves. Remove the cutter.
Whisk the glaze ingredients in a small bowl, and then spread about 1 tablespoon of the mixture over the top and sides of each meatloaf. Bake for 10 minutes, then reduce the heat to 325 degrees F. and bake until cooked through, about 15 minutes more. To serve, ladle some hot marinara sauce into the centers of 4 plates, and set the meatloaves on top.
The pancetta adds a nice flavor note to the meatloaves, but you can leave it out--shape the meat in the cutter right on the baking sheet.
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