Coat slow cooker bowl with nonstick cooking spray. Rub pork loin roast with Sazòn Goya and pepper. Place in prepared slow cooker bowl and pour 3/4 cup water around roast. Cover and cook on HIGH for 6 hours or on LOW for 8 hours.
Heat a panini press or an indoor grill to medium-high. Remove roast from slow cooker to a cutting board. Spread 1 tsp mustard onto 1 side of each roll. Gently break roast apart into large shreds, dividing evenly among rolls.
Top each sandwich with some ham, a slice of cheese and 2 pickle slices. Spread rolls with remaining 6 tsp mustard (1 tsp per roll). Close sandwiches and grill in panini press (or weighed down on indoor grill) for 3 to 4 minutes (2 sandwiches per batch). Serve warm.