Preheat the oven to 350°F (175°C). Grease and flour an 8-inch round cake pan.
In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking soda, and salt.
In a separate bowl, combine the unsweetened almond milk and apple cider vinegar. Let it sit for 5 minutes to curdle, creating vegan buttermilk.
Add the vegetable oil, fresh lemon juice, lemon zest, and vanilla extract to the vegan buttermilk mixture. Stir well to combine.
Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix.
Pour the batter into the prepared cake pan and smooth the top with a spatula.
Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and let it cool in the pan for 10 minutes.
Transfer the cake to a wire rack to cool completely before serving.