Preheat oven to 350°F.
Grease an 9x9-inch baking pan with cooking spray.
In medium-sized bowl whisk together flour, baking soda, baking powder, and salt.
In a separate large bowl, with a mixer, beat together brown sugar, butter, oil, banana and vanilla until smooth.
Add in the flour mixture and stir with a wooden spoon until well blended.
Take about 2/3 of the dough to the prepared pan and press the dough down onto the bottom of the pan in an even layer.
Put the pan in the oven and bake for 10 minutes.
In the meantime, add the chopped walnuts to the reserved dough and stir them in.
Prepare the filling.
In a large saucepan bring together the chopped peaches, orange juice, sugar, and cornstarch.
Bring to a simmer, stirring constantly, until the mixture is thick, about 3 minutes.
Spread the fruit-filling over the baked crust.
Sprinkle the rest of the dough over the filling. This will be a bit sticky, but you’ll get through it. ?
Put back in the oven and bake for 20 minutes, or until the crust is golden.
Cool completely before cutting into bars.