Preheat the oven to 350°F/175°C degrees and grease a round cake pan with a bit of coconut oil or some non-stick baking spray.
In a large bowl, add the soy milk and apple cider vinegar. Stir and let the mixture curdle for 3-4 minutes. This is a vegan buttermilk substitute.
Once the soy milk thickens up, add the sugar, applesauce, lemon juice, and lemon zest to the bowl. Whisk to combine.
In a separate, smaller bowl, mix together wheat flour, spelt flour, baking powder, baking soda, turmeric, and salt.
Fold the dry ingredients into the wet, taking care not to overmix the batter.
Transfer the cake batter into the prepared baking pan and bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool completely before slicing and serving.