Preheat oven to 200°C (180°C fan-forced). Line a roasting tray with baking paper. Quarter one mandarin, then cut each quarter piece in half. Juice the remaining mandarin.
Place pumpkin and mandarin pieces in a bowl and drizzle over oil and sprinkle over spices and salt. Toss pumpkin and mandarin to coat lightly in oil spice mixture. Reserving the mandarin, spread pumpkin over base of lined roasting tray. Roast for 20 minutes. Add reserved mandarin pieces to the roasting tray and return to oven. Cook a further 15 minutes until pumpkin is just tender and the mandarin pieces are golden around edges and skin is easily pierced with a knife.
Meanwhile, place quinoa in a sieve and rinse under cold running water. Place quinoa and 2 cups cold water in a medium sized saucepan over a medium-high heat and bring to boil. Reduce heat to a simmer and cover with lid. Cook for about 15 minutes, or until quinoa is tender and most of the water is absorbed. Remove from heat and set aside for 10 minutes. The quinoa will absorb remaining liquid.
Transfer quinoa to a bowl and cool to room temperature. Add the lemon thyme, parsley leaves, juice, roast pumpkin, and mandarin. Gently toss to combine.
Serve warm or at room temperature.