Preheat oven to 350. Line a 12-count muffin tin with paper cupcake cups (or lightly grease).
In a large bowl, cream butter and sugar until light and fluffy, about 3 minutes. Beat in egg and vanilla.
In a separate bowl, sift together flour and cocoa powder.
In a small bowl, stir baking soda into yogurt (mixture will fizz and expand).
Alternate mixing flour mixture and yogurt into batter, Finally, mix in zucchini. Spoon into muffin cups. Bake 30 minutes, or until cupcakes puff and a tester inserted in the center comes out clean. Cool and enjoy.