1.Preheat oven to 220°C. Line two large oven trays with baking paper.
2.Combine pumpkin, zucchini, onion, capsicum, cumin, coriander, chilli, garlic and oil in a large bowl; season. Place vegetables on trays; roast for 30 minutes or until golden and tender. Drizzle with vinegar.
3.Meanwhile, bring stock to the boil in a large saucepan. Gradually add polenta, whisking continuously. Reduce heat; simmer, stirring, for 10 minutes or until polenta thickens. Stir in 125g of the feta and ⅓ cup of the basil.
4.Serve polenta immediately, topped with vegetables, hazelnuts, remaining feta and remaining basil.