Spinach, sweet potato & lentil dhal

Name: Spinach, sweet potato & lentil dhal
Prep time: 10 min
Cook time: 35 min
Total time: 45 min
Cuisine: Indian
Ingredients: 1 tbsp sesame oil; 1 red onion finely chopped; 1 garlic clove crushed; thumb-sized piece ginger peeled and finely chopped; 1 red chilli finely chopped; 1½ tsp ground turmeric; 1½ tsp ground cumin; 2 sweet potatoes (about 400g/14oz), cut into even chunks; 250g red split lentils; 600ml vegetable stock; 80g bag of spinach; 4 spring onions sliced on the diagonal, to serve; ½ small pack of Thai basil leaves torn, to serve