Honey-roasted sweet potato with red onions

INGREDIENTS

• 750g sweet potatoes , peeled and cut into 4-5cm cubes
• 2 red onions , peeled and cut into thick wedges
• 5 tbsp olive oil
• 1 tsp ground ginger
• 1 tsp ground cumin
• 2 tsp dried chilli flakes
• ½ orange , juiced
• 1 tbsp honey
• a handful of coriander leaves, roughly chopped
• black olives , to serve