Preheat oven to 350F. Butter an 8x8 baking pan and set aside.
Fill a medium-sized bowl with 4 cups of cold water and 2 teaspoons of Kosher salt. Peel, core, and slice apples. Submerge in saltwater solution for 10 minutes. This prevents the apples from rapidly browning.
In a separate medium-sized bowl, mix together all of the topping ingredients except for the cold vegan butter. Using two butter knives or a pastry cutter, cut the butter into the oatmeal mixture until pea-sized chunks are reached.
Pour the water-apple mixture into a colander, and rinse the apples under cold water. Transfer the apples to a large bowl, add the flour and apple pie spice, and mix until thoroughly combined.
Transfer the apple mixture to the prepared baking pan and evenly sprinkle the topping. Gently pat the topping to even it out.
Bake for 40-50 minutes, or until golden brown and bubbly.
Serve warm topped with a scoop of vegan vanilla ice cream or coconut whipped cream, and enjoy!