Remove the pumpkin seeds and fibrous center, then peel away the thick skin carefully.
Cut the pumpkin into thick, evenly sized pieces.
Arrange the pumpkin in a wide saucepan and sprinkle evenly with sugar. Add optional cloves or cinnamon.
Cover and refrigerate for at least 4 hours, preferably overnight, until the pumpkin releases juice.
Place the saucepan over medium-low heat and bring the syrup to a gentle simmer.
Cover and cook for 25 to 30 minutes, then check tenderness with a knife.
If needed, uncover and simmer for 5 to 10 minutes more to lightly thicken the syrup.
Cool the pumpkin in its syrup.
Serve at room temperature or chilled, topped with tahini and chopped walnuts.