Adjust oven rack to lower-middle position and preheat oven to 325 degrees. Grease a 9-square-inch baking pan with vegetable cooking spray. For bars’ easy removal, line pan bottom up the two sides with a 9- by 18-inch strip of heavy-duty foil. Grease foil with vegetable cooking spray.
Mix all ingredients in a medium bowl. Turn into prepared pan and pat down until firmly packed. Bake until golden brown about 30 minutes. Cool to room temperature and put pan in freezer.
When firm, use foil handles to remove bars from pan. Remove foil and use a long, sharp knife to cut bar into 16 1- by 4-inch bars. Can be stored in an airtight container up to 1 week or frozen.