Preheat the oven to 200°C/gas mark 6. Toss the butternut squash in 1 tbsp oil and season. Lay out on a baking tray and roast for 25 minutes or until tender.
Meanwhile, heat 1 tbsp oil in a frying pan. Add the shallots and cumin seeds and cook for 2 minutes until the shallots just start to soften. Add the garlic, chilli, ginger and coriander and cook for a further 2 minutes. Remove from the heat.
Add the butternut, chickpeas and spiced shallot mixture to a food processor and pulse until combined, and the butternut has broken down but there are still chickpea pieces. Transfer to a large bowl and stir in the egg, gram flour and plenty of seasoning until combined.
Put the polenta in a bowl. Shape the butternut mixture into 16 little ‘patties’ and then coat in the polenta until completed covered. Heat the remaining oil in a deep frying pan until it reaches approximately 170°C. Add the patties 4 at a time, turning them over after 2 minutes, then repeat on the other side. Transfer the patties to a kitchen towel-lined plate while you cook the others.
As you cook the other batches, keep an eye on the time – the oil will get hotter, so the patties will probably need to cook for a little less time.
Combine the chopped herbs and lemon juice with the Greek yogurt and season to taste. Serve along with the patties.