Take pineapple and chicken in a bowl and mix well. Add mayonnaise, salt, black pepper powder and mix well.
Apply butter on all the bread slices.
Place a lettuce leaf on buttered side of 2 bread slices and top it with a generous portion of the chicken mixture. Cover each with another slice of bread, buttered side facing down.
Trim the side crusts of the bread slices if you desire and cut into triangles.
Arrange them on a serving platter and serve immediately.