Preheat oven to 325°F (160°C). Line a 9-inch square metal baking pan with foil, extending the foil over the edges.

Spray the foil with nonstick cooking spray.

In a large bowl, whisk together the flour, oatmeal, brown sugar, baking powder, baking soda, and salt.

Stir in the melted butter until well combined.

Set aside 1 1/4 cups of the oatmeal mixture.

Press the remaining oatmeal mixture firmly into the prepared pan to form the crust.

Bake the crust until it's lightly golden brown, about 8 minutes.

Let the crust cool completely.

Stir the chopped cashews into the reserved oatmeal mixture to create the crumb topping.

In a medium bowl, whisk together the flour, brown sugar, instant espresso powder, cinnamon, chili powder, and salt.

Place the chopped chocolate and butter in a large microwave-safe bowl.

Microwave on medium power, stirring every 30 seconds, until the chocolate is softened and starting to melt.

Stir the mixture until the chocolate and butter are completely melted and smooth.

Whisk in the eggs, then stir in the flour mixture until just combined.

Pour the chocolate filling over the cooled crust.

Sprinkle the cashew-oatmeal crumb topping evenly over the filling.

Bake until a toothpick inserted into the center comes out with only a few crumbs attached, about 35-40 minutes.

Let the bars cool to room temperature, at least 1 hour.

Using the foil overhang, lift the bars out of the pan and cut into squares.