Heat the oil in a large pan. Add the butternut squash and cook for 5 mins, stirring over a medium heat. Add the onion and garlic and cook for a further 5 mins until the onion is translucent. Meanwhile make up 2 litres of stock using the stock cubes.
Add the rice and stir for 1 min to heat, then add a ladleful of stock and stir. Cook until the rice absorbs the stock before adding more, a ladleful at a time. Continue cooking for 10-15 mins, stirring, until the rice is almost cooked and all of the stock has been absorbed.
Stir in the peas and dill. Cool half the rice on a baking sheet and when cold put into a freezerproof container and freeze for up to 3 months. Defrost thoroughly and reheat until piping hot.
Cook the remaining rice for a further 4-5 mins until just tender. Season with freshly ground black pepper and serve. Top with parmesan shavings, if desired.