Drain the pineapple and press down on it to thoroughly remove all of the liquid. In a bowl, combine the pineapple, jalapeno, vinegar and mustard seeds. Stir well and season to taste with salt and pepper. Butter a slice of bread, then spread a thin layer of the mustard on top of the butter. Fold a piece of ham to fit the bread and place it on top, followed by a dollop (about 1 tablespoon) of the pineapple mixture. Repeat with the remaining bread slices.