COMBINE butter and pepper in a bowl. Add bread cubes and toss to coat.
ARRANGE in a single layer in an ungreased 15x10x1-in. baking pan.
BAKE at 400° until golden brown, 8-10 minutes, stirring occasionally. Cool.
DIVIDE and layer ingredients in this order in each of four mason jars: dressing, pastrami, coleslaw, tomato, green onions, cheese and salad greens.
ADD croutons to top it off.