Heat oven to 200C/180C fan/gas 6. Toss the butternut squash with 1 tbsp of the olive oil and season. Roast in the oven for 40 mins until tender and caramelised.
Meanwhile, roughly crush the pistachios with the thyme and a pinch of salt using a pestle and mortar, or with the end of a rolling pin. Stir in the lemon juice and remaining oil, and check the seasoning. Spoon the pistachios over the squash to serve.