Heat oven to 200C/180C fan/gas 6.
Spray the aubergine halves with spray oil, then put them cut-side up in a large roasting tin. Add the garlic, coriander and cumin seeds. Roast for 40 mins until the aubergine is tender. Set aside to cool.
Scoop the aubergine flesh into a bowl and discard the skins.
Scrape the spices and garlic from the pan into the bowl.
Add the chickpeas, gram flour, lemon zest and juice, then roughly mash together.
Line a baking tray with grease proof paper.
Shape the mixture into 20 balls and put them on the baking tray. Leave to chill in the fridge for at least 30 mins. [Can be left overnight]
Heat oven to 180C/160C fan/gas 4.
Tip the polenta onto a plate, roll the balls in it to coat, then return them to the tray and spray each one with a little spray oil.
Place into the oven and roast for 20 - 25 mins until crispy, hot and golden.