Preheat oven to 375° degrees F. Line 2 baking sheets with parchment paper or silicone liners; set aside.
In the bowl of a stand mixer, cream together the butter and both sugars until fluffy and smooth, about 1 minute. Beat in the vanilla extract until combined. Lastly, beat in the ground pistachios, flour, and instant pistachio pudding mix powder until combined. Dough may be crumbly; this is normal and perfectly okay.
Using a Tablespoon-size cookie dough scoop, scoop out Tablespoon-size balls of dough into your hand and roll into a ball. The heat of your palm will help hold the crumbly dough together into a cohesive ball. Place 1" apart on the baking sheets.
Bake for 10-13 minutes or until light golden brown and set. Cool completely on the baking sheets as the cookies are very tender and delicate while they cool.
After the cookies cool, make your glaze. In a small bowl, whisk together the confectioners' sugar, lemon zest and lemon juice until combined. Dip the tops of the cookies into the glaze and allow the excess to drip off. Return the glazed cookies to a wire rack and allow glaze to set before storing or serving.