Preheat the oven to gas 7, 220°C, fan 200°C. Cut the vegetables into wedges about 2.5cm (1in) thick and about 8cm (3 1/2in) long. Arrange in a large roasting tin in a single layer. Nestle in the garlic, cloves, drizzle over 1 tbsp oil and season. Put the tin on the bottom shelf of the oven and reduce the temperature to gas 6, 200°C, fan 180°C. Roast for 35 minutes, shaking the tray a few times during cooking, until the vegetables are golden. Meanwhile, rub the chicken with the remaining oil. Combine the polenta, Parmesan and a little seasoning on a large plate, then roll the chicken in the mixture, until evenly coated. Transfer to a baking sheet and arrange on the top shelf of the oven. Cook for for 30 minutes, or until the crust is golden, there is no more pink meat and the juices run clear. Using a slotted spoon, remove the garlic cloves from the roasting tin, and when cool enough to handle, squeeze the pulp into a bowl, discarding the papery skins. Mash with a fork until smooth, then add the yogurt and stir until combined. Season to taste. Drain the vegetable chips on kitchen paper. Serve with the chicken, garlicky yogurt dip and some lemon wedges for squeezing over.