Grease 13x9-inch baking pan.
In a large bowl, combine gluten free flour, oats, brown sugar, baking soda and salt and mix well.
Add butter mix at with a pastry blender or two knives until crumbly. Could also try the paddle attachment of your stand mixer but a hand mixer is not recommended.
Reserve 3 cups of the crumb mixture for the topping.
Press remaining crumb mixture in bottom of the greased pan.
Preheat the oven to 350°F and bake for 10 minutes once the oven is heated.
In a Microwave safe bowl, combine caramel bits and 2 tablespoons milk.
Microwave the caramel and milk in 30 second intervals, stirring between each 30 seconds until the caramel is melted and smooth. This will take 1 ½-2 Minutes.
Remove the crust from the oven and sprinkle evenly with chocolate chips and nuts, if using.
Drizzle the melted caramel over the chocolate chips and nuts and sprinkle evenly with reserved crumb mixture.
Bake the bars for 18 to 22 minutes or until golden brown.
Cool 1 hour on the counter until completely cooled.
Refrigerate for 1 to 2 hours or until filling is set.
Cut into bars.