Preheat the oven to 375 degrees. Line a 9 x 15 lipped baking pan with parchment paper and spray the pan with non stick cooking spray. Set aside.
In a small bowl, combine the flax meal and water. Stir together until well mixed, then set aside to thicken, about 5 minutes. Once thickened, add the flax mixture into a large bowl, along with the pumpkin puree and almond milk. Using a hand mixer on medium low speed, blend ingredients together then slowly add the dry cake mix and pumpkin pie spice and beat until a smooth and thick batter forms.
Pour the batter into the pan and spread evenly with a spatula. Bake 15-17 minutes or until the cake is firm and a toothpick inserted into the center comes out clean. Remove from the oven and allow to cool for 5-10 minutes.
Dust a kitchen towel generously with the powdered sugar. Place the cake face down on the towel with one of the shorter ends of the cake facing you. Carefully peel off the parchment paper, then slowly roll up the cake and the towel together. Place in the refrigerator while you prepare the filling.
In a medium sized bowl, combine the vegan cream cheese, non dairy butter and vanilla until smooth. Slowly add the frosting mix and a pinch of salt and continue mixing until the filling is smooth and creamy.
Remove the cake from the refrigerator and unroll slowly. Spread the filling evenly over the cake then roll the cake again, wrap in plastic wrap and refrigerate at least one hour. Sprinkle the top of the roll with powdered sugar before serving.