Skin and deseed the pumpkin, cut the flesh into 2 cm (¾ inch) squares and put them in a roasting tin. Drizzle with olive oil, scatter over the thyme and season with salt and pepper. Roast the pumpkin in a preheated oven, 190°C (375°F), Gas Mark 5, for 25 minutes or until cooked though. Remove the pumpkin from the oven and allow to cool slightly.
Meanwhile, make the dressing. Whisk together the mustard, vinegar and oil and set aside.
Put the mixed leaves in a large salad bowl, add the cooked pumpkin and crumble in the feta. Drizzle over the dressing and toss carefully to combine. Transfer the mixture to serving plates, garnish with toasted pine nuts and serve immediately.