Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners or lightly grease it.
In a medium bowl, sift together the flour, cocoa powder, baking soda, and salt. Whisk until combined.
In a large bowl, whisk together the sugar, vegetable oil, eggs, buttermilk, vanilla extract, white vinegar, green gel food coloring, and optional matcha powder until smooth and vibrant.
Slowly add the dry ingredients to the wet mixture, folding gently with a spatula until just combined. Do not overmix.
Divide the batter evenly among the 12 cupcake liners, filling about ⅔ full.
Bake for 20 to 22 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Remove cupcakes from the oven and let them cool in the pan for 5 minutes. Then transfer to a wire rack to cool completely before frosting.
To make the frosting, beat the softened cream cheese and unsalted butter together until smooth and fluffy.
Gradually add the powdered sugar, mixing on low speed to avoid a sugar cloud.
Add lemon juice and beat until light and spreadable.
Frost each cupcake generously using a piping bag or spatula. Optionally, decorate with green sugar crystals or edible gold glitter.