Combine gelatin and water in a small bowl and place over double boiler, stirring until gelatin dissolves. Remove from heat and set aside.
In a standing mixer with paddle attachment, cream together cream cheese and sugar until combined and smooth. Set aside.
In a food processor, add lemon juice with avocado and process until smooth.
Add avocado mixture to cream cheese mixture and mix together until well combined.
Place whisk attachment on mixer. With mixer running, gradually add the warm gelatin to the avocado-cream cheese mixture and whisk together until well combined.
Add the yogurt and mix together until well combined again. Set aside.
Using a hand-held mixer or standing mixer with whip, whip whipping cream to soft peaks.
Fold whipping cream into the avocado mixture until well combined.
Pour mixture onto prepared pistachio shortbread crust and allow to set in the refrigerator overnight to completely set.
Once cool, cut into 2-inch squares.
Top with finely chopped pistachios to liking.
For the Pistachio Shortbread Crust
Preheat oven to 350 degrees F. Line an 8-inch-square cake pan with parchment paper.
Using a food processor, pulse together the shortbread, pistachios, sugar, salt, and grated lemon peel until finely broken up. Add melted butter and pulse mixture again until small clumps form.
Press crust into prepared cake pan. Refrigerate crust for about 10-15 minutes before baking to set up. Bake for about 15-20 minutes or until crust begins to brown slightly. Allow to cool completely before adding the avocado cheesecake mixture.
Alternative method: Bake the shortbread crust in paper muffin/cupcake liners for about 5-7 minutes and then add a large scoop of the avocado cheesecake mixture to make mini cheesecakes. Place the muffin/cupcake liners in muffin/cupcake tins to allow cheesecakes to hold their shape while setting in the refrigerator. There may be extra avocado filling from the cheesecake recipe listed above.
Large avocados are recommended for this recipe. A large avocado averages about 8 ounces. If using smaller or larger size avocados adjust the quantity accordingly.