Heat oven to 350°F. Grease 13x9-inch pan with cooking spray. In a large bowl, beat brown sugar, butter, and egg with an electric mixer on medium speed, or mix with a spoon. Stir in flour and oats. Spread evenly in the pan (helps to use your hands - just wet them to prevent sticking).
Bake 15 to 20 minutes or until light golden brown. Meanwhile, in a 1-quart saucepan, heat caramels and heavy cream over low heat, stirring occasionally, until caramels are fully melted. Stir in peanut butter.
Pour caramel mixture evenly over the crust. Sprinkle on chocolate chips, peanuts, and pretzels. Press toppings into the caramel slightly, and cool until chocolate is set. Cut into 24 bars. Enjoy!