Mix the wasabi with the cream cheese in a small bowl. Spread the bread slices with a thin, even layer of the mixture.
Cut the avocado in half lengthwise and twist the 2 halves apart and remove the pit. Use a spoon to remove the avocado flesh in 1 piece. Slice each avocado half in 1/8-inch slices. Place the avocado slices in a bowl and squeeze juice from 1/2 lemon over avocado slices and toss gently.
Cover each bread slice with a single layer of avocado slices. Top with a piece of salmon. Serve as soon as possible.