In medium bowl, combine chicken, apple, cucumber and cashews; mix well. Add 2 tablespoons mayonnaise, onion powder, salt and pepper; mix well.
Spread about 1/2 cup chicken mixture on each of 4 slices of bread. Arrange spinach leaves over chicken mixture. Spread each remaining bread slice with 1 teaspoon mayonnaise; place, mayonnaise side down, over spinach leaves.