Preheat your oven to 350°F (175°C). As the oven warms up, grab a 9 x 13-inch baking dish and spray it with baking spray on all sides to ensure easy removal later.
In a large mixing bowl, combine the cake mix, pudding mix, eggs, vegetable oil, and water. Use a whisk or electric mixer to blend the ingredients until the batter is smooth and well combined. Keep mixing until there are no lumps.
If you desire that vibrant green color, add 1 to 3 drops of green food coloring to the batter. Mix it in until you achieve your desired shade.
Pour the batter into the prepared baking dish, spreading it into an even layer with a spatula. It should fill the dish nicely.
Sprinkle the chopped pistachios evenly over the top of the cake batter. These will add a lovely crunch and flavor once baked.
Place the cake in the oven and bake for 25 to 30 minutes. You’ll know it’s done when the center is puffed up and a toothpick inserted into the middle comes out clean.
Once baked, let the cake cool in the pan for a few minutes while you prepare the glaze. This cooling step is essential for letting the flavors meld together.
In a medium mixing bowl, combine the powdered sugar, warm water, melted butter, and either almond extract or pistachio extract. Whisk until the mixture is very smooth and free of lumps.
Using a toothpick or wooden skewer, poke dozens of holes over the entire surface of the cake. This will allow the glaze to seep into the cake, creating an incredibly moist treat.
Pour the glaze evenly over the top of the cake, using a spatula to help it run into the holes. Allow the remaining glaze to cool and set on the cake. Once set, the cake is ready to cut and serve!