Combine first 4 ingredients in a large bowl; mix gently. Set aside.
Add bread slices to food processor bowl; process until crumbs are fine. Remove breadcrumbs from processor bowl; set aside. Place cookies in processor bowl; pulse 8 times or until crumbs are coarse.
Combine cookie crumbs, breadcrumbs, and butter in a medium bowl; toss with a fork. Sprinkle 1/2 cup crumb mixture in bottom of 1 1/2- quart casserole or soufflé dish coated with cooking spray. Top with half of nectarine mixture; sprinkle with 3/4 cup crumb mixture, and top with remaining nectarine mixture. Sprinkle with remaining crumb mixture.
Cover and bake at 350° for 35 minutes or until fruit is tender. Uncover and bake 15 additional minutes or until bubbly. Serve warm.