Heat oven to 200C/180C fan/gas 6. Put the red onions, peppers and courgettes in a large roasting tin, toss in 2 tbsp oil and season. (You may need to do this in 2 tins.) Pop in the oven and cook for 25 minutes until the veg is tender and beginning to turn golden.
Meanwhile, cook the rice following pack instructions. Whizz together the parsley, cashew nuts, remaining oil, the garlic and seasoning to make a pesto. Stir the chickpeas and halloumi into the roasted veg and cook for 10 minutes more. Fork the parsley pesto through the rice, spoon over the veg and serve.