Preheat oven to 325 F. Lightly grease a 9 x 13 in baking pan.
In a medium bowl, beat butter, pumpkin, honey, and vanilla until smooth. In another medium bowl, combine oats, flour, salt, and cinnamon. Add dry mixture to liquid and gently stir until a ball of dough forms. Do not over-mix.
Press shortbread dough into prepared baking pan. Prick dough with a fork. Bake at 325 F 30 minutes or until golden brown and firm to the touch. Immediately cut shortbread into 12 squares. Let shortbread cool completely in pan on a wire cooling rack.
Once shortbread is cooled, remove bars from pan and prepare the caramel topping: In small saucepan over medium-high heat, bring butter and honey to a boil, stirring constantly until caramel is thickened. Remove from heat and stir in salt. Immediately drizzle caramel over shortbread bars and let bars stand 5 minutes before serving.
Store squares in an airtight container at room temperature up to 3 days.