Place cupcake liners into muffin tins and spray the inside of the liners with a little oil. (This will allow you to easily take the paper off the cupcake.)
Mix the dry ingredients (flour, sugar, baking soda, and salt) in a large mixing bowl.
Measure out the wet ingredients (plant milk, lemon juice, oil, lemon zest, and vanilla extract) in a separate container.
Add the wet ingredients to the dry and stir with a whisk.
Stir until the wet and dry ingredients have combined, but don't over-mix.
Scoop out about 1/2 cup of the cake batter at a time and fill the cupcake liners about 3/4 of the way full.
Bake for 22 minutes at 375° F (190° C) until the tops of the cupcakes appear dry and spring back up when touched.
Allow it to cool completely before filling (if you choose) or frosting.
To make lemon frosting
Soften vegan butter until it reaches near room temperature.
Whip butter with an electric mixer using the whisk attachment for 1 minute.
Add powdered sugar 1/2 cup at a time whipping for about 30 seconds between each scoop.
Add 1 tsp lemon extract and the zest of one lemon then continue to whip for another minute until light and airy.
If needed, slowly add a small splash or two of dairy-free milk while whipping the buttercream until the desired consistency is achieved.
Notes
Make sure your cake is completely cooled before frosting it or your buttercream will melt. (You can put the cakes in the refrigerator to help them cool faster if you need to).