Once cake is mixed according to package directions, add the zest of two lemons. Pour 1/3 of the batter into a microwave-safe 9x9 baking dish and microwave for 2-4 minutes, just until the cake springs back to the touch. Crumble the cake into a large microwave-safe bowl, and continue to microwave until the cake is fully cooked. Crumble and cool fully. Cook the remaining cake batter in like manner.