Preheat oven to 350 degrees. Coat an 8x8 glass baking dish with coconut oil cooking spray.
Prepare the apples by melting 1 teaspoon of butter over medium heat in a small skillet. Add the apple and cook for one minute, tossing to coat evenly with the butter. Sprinkle with ½ tablespoon brown sugar, 1 teaspoon cinnamon, 1 teaspoon apple cider vinegar, and 1 teaspoon flour then cook for another 2 minutes, stirring occasionally; set aside to cool.
Make the brown butter in a medium saucepan, melt 6 tablespoons of butter over medium heat. Cook until the butter turns golden brown and starts smelling like nuts. Whisk in 3/4 cup brown sugar and set aside to cool for 5 minutes.
Mix the flour, baking powder, cinnamon, and salt, until well combined.
Once the butter/sugar mixture has cooled to room temperature, whisk in the oil, vanilla extract, and eggs, one at a time. Slowly add the flour mixture to the egg mixture until just combined. Fold in the finely diced apples.
Pour the cake batter into the prepared baking dish then sprinkle the top with chopped pecans.
Place into the oven and bake for 25-30 minutes or until a wooden skewer inserted into the center comes out clean.
Cool in the pan for 5 minutes before slicing and placing the pieces on a wire cooling rack.
Make the glaze by sifting the powdered sugar into a small bowl. Gradually stir in the apple juice, one teaspoon at a time, until it reaches the consistency of a thick glaze. It should be pourable, but not liquid.
Drizzle over the cooled cake bars at an angle. Serve and enjoy.