Heat the oven to 350 degrees.
Spray a Bundt pan with cooking spray.
Lightly dust the pan with flour to help the cake release more easily.
In a large bowl with an electric mixer, mix together the butter and the sugar, beating them together until they are light and fluffy.
Add the eggs one at a time, using the mixer to beat well after each addition.
Add the vanilla and the lemon zest, mixing well.
Using a separate medium sized bowl, combine the flour, baking powder, and salt.
Whisk these dry ingredients together to combine them.
Add one third of the dry ingredients mixture to the butter and sugar mixture, using the electric mixer on medium speed to thoroughly combine them.
Add one third of the 7 Up and mix again.
Take half of the remaining dry mixture and blend it into the larger bowl, mixing well.
Add half of the remaining 7 Up, blending well after adding it.
Finally, add the last of the dry ingredients to the larger bowl, mixing well, and then add the remaining 7 Up, mixing again. The mixture should be light, fluffy and creamy.
Pour the batter into the prepared pan and smooth the top with a rubber spatula.
Place the pan in the center of the preheated oven and bake the cake for 60-65 minutes, or until a cake tester inserted in the middle of the cake comes out clean.
Allow the cake to cool for about ten minutes on the counter.
Gently remove the cake from the pan onto a wire rack to cool completely.
While you are waiting for the cake to cool, you can create the glaze.
In a small bowl with a wire whisk, combine the powdered sugar, lemon juice, and salt. Whisk in the 7 Up a teaspoon at a time, until the glaze has the texture of yogurt, slightly thickened but still rather runny.
When the cake is completely cooled, after about an hour and a half, drizzle the glaze over the top so that it runs down the sides of the cake.
Cut into slices and serve.