Heat a large, deep frying pan over a medium/high heat and add the olive oil, onion, grated pumpkin, zucchini and a good pinch of salt.
Cook without any colour, stirring, for 5 minutes then add the rice and cook stirring for a further 1 minute then start ladling in the stock, a little at a time and stiring constantly to allow the stock to absorb and rice to become creamy.
Keep doing this until the risotto is creamy and the rice cooked. You want it loose but not wet. Turn the heat off and stir through the cheese then allow to cool completely in the fridge. Overnight is best.
Roll golf ball size balls of the risotto and place onto a plate.
Pour half the coating mix into a shallow bowl and the milk into another bowl
Gently toss the balls through the flour then the milk and back into the flour again, allow the balls to sit for at least 10 minutes before cooking.
Heat the oil in a small saucepan over a medium/high heat for 3-4 minutes. When hot enough, add the balls in batches of 4 or 5 and cook for approx. 3 minutes, turning throughout cooking until they are golden and crisp.
Serve the arancini with a little parmesan finely grated over them and the lemon to serve.