Core and dice half a Granny Smith apple into small pieces. Weigh or measure the light brown sugar and white sugar into a bowl and set aside. In another bowl, weigh or measure the flour, oats, baking powder, cinnamon, ginger, and kosher salt. Run a whisk through the dry ingredients to blend.
Cube the room-temperature butter and add it to the mixer bowl. Mix on medium speed for 1 to 2 minutes, until creamy with soft peaks.
Add both sugars and mix on medium speed for 3 minutes so the sugars incorporate into the butter.
Add the egg, vanilla bean paste, and apple juice. Mix until blended, then scrape down the sides and across the bottom of the bowl.
Turn the mixer to low and add the flour mixture in thirds. Mix until just incorporated.
Add the golden raisins, chopped walnuts, and diced apple pieces. Mix for a few seconds. If needed, use a sturdy one-piece spatula to distribute them evenly throughout the dough.
Loosely cover the mixer bowl and refrigerate the dough for 30 minutes. Chilling gives the oats time to absorb moisture and firms the dough, making it easier to scoop and helping the cookies hold their shape.
Preheat the oven to 350°F (175°C or 180°C) and line two cookie sheet pans with parchment paper.
Using a medium-sized cookie scoop, place 12 mounds of dough onto a prepared pan. Place a small piece of parchment paper over each mound and use the bottom of a flat-bottomed glass to gently flatten it into a thick disk.
Bake for 12 to 14 minutes. The tops should look set and no longer shiny, but the cookies will still be soft. Leave them on the pan for 3 minutes before transferring them to a wire cooling rack.