Cauliflower & potato curry

INGREDIENTS

• 2 tbsp vegetable oil
• 1 large onion , chopped
• large piece ginger , grated
• 3 garlic cloves , finely chopped
• ½ tsp turmeric
• 1 tsp ground cumin
• 1 tsp curry powder , or to taste
• 227g can chopped tomatoes
• ½ tsp sugar
• 1 cauliflower , cut into florets
• 2 potatoes , cut into chunks
• 1 small green chilli , halved lengthways
• squeeze lemon juice
• handful coriander , roughly chopped, to serve
• naan bread and natural yogurt, to serve