Preheat oven to 180°C/160°C fan forced. Line 3 baking trays with baking paper. Spread pistachios over a prepared tray. Roast for 5 minutes or until lightly toasted. Transfer to a plate to cool. Process until finely chopped. Return to the plate and set aside.
Increase oven to 200°C/180°C fan forced. Place sweet potato in a single layer on another prepared tray. Spray with olive oil. Roast, turning once during cooking and adding garlic for the last 20 minutes of cooking time, for 45 minutes or until golden and tender.
Spread chickpeas over remaining prepared tray. Roast for 10 minutes or until slightly dried. Set aside to cool to room temperature.
Process the sweet potato and chickpeas until well combined. Squeeze the garlic flesh from the skins and discard skins. Add garlic flesh, quinoa, tahini, lemon rind and paprika to the processor. Process until well combined and almost smooth, scraping down sides when necessary. Season to taste. Transfer mixture to a bowl.
Roll level tablespoonfuls of mixture into balls. Make an indentation in the centre of each ball and add a piece of feta. Roll to enclose. Roll balls in pistachio to lightly coat. Store in an airtight container in the fridge for up 4 days.
