Preheat oven to 180°C/360°C.
Place cauliflower onto a large baking tray lined with foil. Brush liberally with half the chili sauce. Sprinkle with half the paprika and a pinch of salt. Turn the pieces over and repeat with the remaining paprika and a little more salt.
Roast in the oven for 45 minutes or until tender and starting to char at the edges. Transfer to a serving plate and sprinkle with pistachios.