Preheat the oven to 350° and spray a 9x13 baking dish with cooking spray.
In a large bowl, cream the butter, sugars and peanut butter until light and fluffy.
Beat in the egg and vanilla. Combine the flour, oats, baking soda and salt; gradually beat into creamed mixture and mix well. Spread mixture into prepared pan, pressing down with your hands. Sprinkle with chocolate chips and slightly press them into the bars.
Bake for 18-25 minutes or until lightly browned. Do not overbake! Cool on a wire rack for 10 minutes.
Combine icing ingredients adding more milk if necessary to reach a drizzle consistency. Drizzle over the top. Cool completely and then cut into bars. Store in an airtight container.
Notes
Note: If all you have are old-fashioned oats you can put them in the blender for a couple of pulses to make quick oats. Source: Taste of Home