Line an 8x8 inch baking pan with parchment paper, leaving some overhang on the sides for easy lifting.
Pulse the ½ cup shelled pistachios in a food processor until they're finely chopped, like crumbs.
In a mixing bowl, combine the almond flour, ground pistachios, granulated sweetener, and salt.
Stir in the melted butter, egg yolk, vanilla extract, and a drop of green food coloring (if using) until a soft dough forms.
Press this mixture evenly into the bottom of your prepared pan to create a firm crust.
Clean out your food processor.
Add the ½ cup pistachios and avocado oil, then process until it turns into a relatively smooth pistachio butter.
Add the room temperature cream cheese (¼ cup at a time), blending until completely smooth after each addition. Mix in the Greek yogurt and blend again.
Next, add the powdered sweetener and salt, blending until fully incorporated.
Finally, add the egg, vanilla extract, almond extract, and optional green food coloring. Pulse just until smooth; be careful not to overmix once the egg is added.
Gently pour the creamy pistachio filling over the prepared crust in the pan.
Bake in a preheated oven at 325°F (160°C) for about 22 minutes, or until the filling looks set and slightly firm.
Remove the pan from the oven and let the bars cool completely on a wire rack – patience is key here!
While the bars cool, heat the heavy cream in a small saucepan over low heat or in the microwave until it's hot but not boiling.
Remove from heat, add the sugar-free chocolate chips, and stir continuously until they are fully melted and create a smooth, glossy chocolate ganache.
Pour the melted chocolate ganache evenly over the completely cooled pistachio bars.
For an extra touch, you can pipe thin green stripes (using melted sugar-free white chocolate mixed with cream and green food coloring) over the chocolate, then drag a toothpick through them in the opposite direction to create a beautiful pattern.
Sprinkle the chopped pistachios around the edges.
Refrigerate the bars for several hours (at least 2 hours) until the chocolate topping is firm and set.
Once chilled, use the parchment paper overhang to lift the entire slab from the pan. Slice into 16 neat bars with a sharp knife and savor your refreshing, healthy summer treat!