Prepare the apple filling by cooking chopped apples with maple syrup, pumpkin pie spice, salt, water, and cornstarch until thickened. Let cool.
Mix the cupcake batter by combining flour, cornstarch, pumpkin pie spice, baking powder, salt, brown sugar, non-dairy milk, oil, and vanilla. Fill cupcake liners halfway.
Spoon apple filling into the center of each cupcake batter.
Bake at 350°F (175°C) for 20-25 minutes until golden and cooked through. Cool completely.
Prepare frosting by beating non-dairy butter, powdered sugar, non-dairy milk, and vanilla until smooth. Frost cooled cupcakes.
Notes
Ensure apples are peeled and chopped into 1/4" cubes for even cooking.