Roast root vegetable & green lentil soup

INGREDIENTS

• 250g Chantenay carrots , halved lengthways
• 1 parsnip , peeled and cut into small chunks
• 250g swede , peeled and cut into small chunks
• 1 red onion , cut into thin wedges
• olive oil
• a pinch of dried chilli flakes
• 2 tsp ground cumin
• 200g green lentils
• 1½l vegetable stock
• a small bunch of coriander , chopped