In a bowl, combine the butter, salt and pepper. Add the cubed bread and toss to coat. Arrange in a single layer in an ungreased 15 x 10 x 1 inch baking pan. Bake at 400 degrees for 8-10 minutes or until golden brown, stirring occasionally. Cool.
In a large bowl, layer half of the salad greens, pastrami, tomato, sauerkraut, onions and dressing; repeat layers. Sprinkle with croutons and Swiss cheese.