Preheat oven to 350 degrees. Line the bottom of a 5 x 9" loaf pan with a piece of waxed paper. (With a pencil, trace the bottom of the pan on a piece of waxed paper and cut out with scissors.) Spray the pan, and waxed paper with non-stick baking spray. Set aside.
In a mixing bowl, combine the flour, pudding mix, baking powder, baking soda, and salt. With a stand or hand mixer, combine the eggs, sugar, butter, vanilla, lemon extract, lemon juice, oil and yogurt. Mix until evenly combined. Gradually add the dry ingredients to the wet, stopping to scrape down the sides of the bowl. Add the lemon zest, and mix until just combined. Pour the batter into the prepared loaf pan. Bake for 55 minutes, or until center is fully set, and a toothpick inserted comes out crumb free.
After baking, let cool in the pan for 5-10 minutes. Run a knife around the sides of the pan, invert and remove from the pan, removing the waxed paper from the bottom. Cool completely on a cooling rack.
For the frosting: Combine the butter, lemon juice and lemon extract with hand or stand mixer. Gradually add the powdered sugar, and beat until smooth and creamy. Evenly spread the frosting over the top of the loaf. Refrigerate to let frosting set completely before slicing. Refrigerate any leftovers in an airtight container.