Preheat the oven to 160°C (320°F). Grease the springform pan and line the bottom with baking paper.
To make the crust, crush the digestive biscuits in a food processor until they resemble fine crumbs. In a bowl, mix the crumbs with the melted butter until well combined. Press the mixture firmly into the bottom of the prepared pan to create an even layer.
Bake the crust for 10-12 minutes, then let it cool.
In a food processor, combine the cooked beetroot, feta cheese, cream cheese, Greek yogurt, sugar, eggs, vanilla extract, and lemon juice. Blend until smooth and creamy. Taste the mixture and adjust the sweetness if needed.
Pour the beetroot filling over the cooled crust in the springform pan. Smooth the top with a rubber spatula.
Bake the cheesecake in the preheated oven for 45-50 minutes or until the center is set but still slightly wobbly. Turn off the oven and leave the cheesecake inside for another 10 minutes.
Remove the cheesecake from the oven and let it cool to room temperature. Once cooled, refrigerate for at least 4 hours or overnight for better flavor and texture.
Before serving, sprinkle the top of the cheesecake with the chopped pistachios and garnish with additional beetroot slices if desired.