Preheat oven to 350 degrees F. Line a 13x9x2-inch baking pan with foil, extending foil over edges of pan. Grease foil; set aside. In a bowl, combine flour, oats, brown sugar, baking soda, and salt. Add melted butter and mix until crumbly. Reserve half of crumb mixture (about 2 1/2 cups) for topping. Press remaining crumb mixture into bottom of prepared baking pan.
In a microwave-safe bowl, combine caramels and milk. Microwave on 50% power (medium) for 4 to 6 minutes or until caramels are melted and mixture is smooth, stirring twice.
Sprinkle chocolate pieces and pecans over crust in pan. Drizzle evenly with melted caramel mixture; sprinkle with reserved crumb mixture.
Bake for 20 to 25 minutes or until light golden brown. Cool in pan on a wire rack. Using the foil, lift the uncut bars out of the pan. Cut into bars.