Preheat oven to 350 degrees F. Cook pasta to al dente, according to package directions. Drain well.
In a large bowl, stir together soup, milk, mayonnaise, and pepper. Stir in cooked pasta, vegetables, and chicken.
Spoon into an ungreased 3 quart rectangluar glass baking dish. In a medium bowl, toss bread cubes with melted butter and garlic powder; sprinkle over pasta mixture.
Bake uncovered, 30-35 minutes, until heated through and bread is golden. Let stand 10 minutes before serving.