Spread a thin layer of salad dressing on one side of each slice of bread. Place two slices of Spam side by side on 5 of the slices of bread. They should cover the slices perfectly. Place two slices of cheese over each layer of Spam, so that they cover the whole slice of bread. Place slices of pineapple over the cheese, trimming square to fit the sandwiches. Top with remaining slices of bread with the salad dressing on the inside. Trim the crusts if desired, and cut each sandwich into 4 equal squares.