Preheat the oven to 400 degrees. Prepare a large rimmed baking sheet with aluminum foil, spritzing with nonstick cooking spray.
Open the French bread loaves and on one side of each sandwich, brush the bread with pickle juice. On the other side, spread with mustard.
On the bread, place a layer of pork roast, ham, and cheese. Cover the cheese with the other side of the bread.
If desired, brush the top of the bread with additional pickle juice.
With both sandwiches completed and placed on the rimmed baking sheet, place another baking sheet on top of the sandwiches, pressing down lightly.
Place the sandwiches in the oven with the additional baking sheet remaining on top. Place a cast iron skillet on top.
Bake for about 20 minutes or until the bread is toasted and the cheese has melted.
Slice the sandwich and serve.