Toss the pumpkin pieces in 1 tablespoon oil, season and spread out in a roasting tin. Roast in a preheated oven, 200°C (400°F), Gas Mark 6, for 30 minutes.
Mix the remaining oil with the lemon juice and mint. Spoon the mixture over the feta cheese and set aside.
Add the walnuts and the tomatoes to the pumpkin and bake for a further 10 minutes.
Serve the pumpkin with the walnuts and tomatoes and any pan juices. Crumble over the cheese and pour over the marinade. Serve with the spinach leaves and garnished with shredded mint.