Before you start, preheat oven to 220°C (or 200°C fan bake). Bring a full kettle to the boil.
Pat chicken dry and toss with Italian spices, pumpkin and oil on 1-2 lined oven trays. Season well with salt and pepper and roast for about 25 minutes, until cooked through. Swap trays halfway through cooking. Rest.
Combine risotto stock spiced and boiling water measure in a heat-proof bowl and cover. Prep leek, garlic and courgette.
Heat oil in a large pot (with a lid) on medium-high heat. Add leek to pot with salt and cook for about 3 minutes, until softened. Add rice and garlic and cook for 1 minute, stirring constantly.
Add stock to rice and stir well. Reduce heat to low-medium, cover, and gently simmer for 18-20 minutes, stirring occasionally, until rice is tender and liquid has absorbed. Add more water if risotto becomes too dry.
Thinly slice cooked chicken. Add chicken and any resting juices along with pumpkin, courgette, butter and first measure of Parmesan to cooked risotto. Season to taste with salt and pepper.
Serve risotto topped with remaining Parmesan and walnuts.