Preheat oven to 350°F (175°C). Grease and flour a 9×13 inch baking pan.
For the crust/topping: Combine flour, oats, brown sugar, granulated sugar, baking powder, and salt in a bowl. Cut in cold butter until mixture resembles coarse crumbs.
Press half of the mixture into the prepared pan to form the crust. Reserve the remaining mixture for the topping.
For the filling: In a separate bowl, combine pumpkin puree, sweetened condensed milk, eggs, vanilla extract, and chai spice blend. Mix well.
Pour the pumpkin filling over the crust. Sprinkle the remaining oat mixture evenly over the filling.
Bake for 30-35 minutes, or until the topping is golden brown and the filling is set. A toothpick inserted into the center should come out clean.
Allow the bars to cool completely before cutting into squares.