Preheat oven to 350˚F. Spray a 15x10x1-inch baking pan generously with baking spray. Use a paper towel to spread the spray to all of the edges.

In a medium-large microwave-safe bowl, combine the butter and the water. Cook on high power for 1-2 minutes, until the butter is melted. Set aside to cool for 5 minutes.

Add the sugar, eggs and Greek yogurt. Whisk well to combine.

Add the poppy seeds, baking powder, salt, baking soda and lemon zest. Whisk until everything is incorporated.

Add the flour and whisk just until the mixture is smooth and lump-free.

Transfer to prepared pan. Bake until light golden brown and a toothpick inserted in the center comes out clean, 18-22 minutes. Remove to a cooling rack while you make the icing.

Combine butter and 3 tablespoons of milk (or half and half) in a large microwave-safe bowl. Cover with a damp paper towel and microwave on high powder for 1 minute or until the butter is melted.

Add 2 cups of the powdered sugar, the lemon juice and the vanilla. Stir until well combined then add the remaining powdered sugar and whisk until nice and smooth. Icing should be thick, but spreadable. If it’s too thick add more of the millk, if too thin add a bit more powdered sugar.

Spread about 1 cup of the icing over the warm cake and set aside to cool for at least 45 minutes. When cool, spread the remainder of the icing over the cake with a butter knife or angled spatula, swirling the icing decoratively. Sprinkle lightly with more poppy seeds.