Combine the flour, baking soda, baking powder and salt in a bowl and set aside.
In another bowl, cream the butter and sugar until pale and fluffy. Add the eggs, vanilla extract, lemon and lime juice and zests, and beat until combined. Stir in the grated zucchini and lemon squash.
Add the buttermilk and flour mixture to the wet mixture, alternating in thirds and stir lightly after each addition. Do not over-stir or the cake will be dense. Stir just until combined, a few small lumps are okay.
Pour the batter into the greased baking pan and bake for 30-35 minutes or until a toothpick inserted into the center of the cake comes out clean. Let the cake cook completely.
While the cake is baking make the frosting: Combine all the ingredients, except for the powdered sugar, in a mixing bowl and beat until combined. Add the powdered sugar gradually, beating until combined.
Frost the cake and cut into squares.
Notes
This recipe can also be made in bread loaf pans if you prefer to cut it into slices.
Recipe by The Daring Gourmet at https://www.daringgourmet.com/lemon-lime-zucchini-cake-with-lemon-lime-cream-cheese-frosting/