Prepare the pan and preheat oven - Preheat the oven to 300 degrees F and line a 8-inch square metal baking pan with parchment paper. Leave some overhang on all sides for easy removal later. Set aside.
Make the shortbread crust - Add the melted vegan butter, sugar, vanilla to a medium sized bowl and stir. Now add the flour and stir until combined. Press evenly into the prepared pan. Place in the oven and bake for 15 minutes, then remove and set aside. Turn the oven up to 350 degrees F.
Make the apple filling - In a large bowl, combine the apples, sugar, flour, cinnamon and nutmeg and stir until the apples are coated. Set aside.
Make the topping - Stir the oats, flour, brown sugar and cinnamon in a medium sized bowl (I use the same bowl I made the crust in). Use a pastry cutter (or your hands) to cut in the cold vegan butter until the mixture looks like coarse crumbs.
Put together and bake - Layer the apple mixture evenly over the warm crust. Press them down a bit to make them all fit. Sprinkle the topping over the apples and bake for 30-35 minutes until golden brown.
Let cool and serve - Remove from oven and let cool for about 30 minutes at room temperature, then move to the refrigerator and let chill for 1 hour, if possible. You can also serve warm, they just won't hold together as well. Use the parchment overhang to lift the bars out of the pan. Cut into squares with a large heavy knife. Drizzle with some vegan salted caramel before serving. Enjoy!