Heat the coconut oil in a large frying pan or saucepan over a medium heat. Add the spring onion tops and cook for 2-3 minutes. If using a regular onion instead, gently cook it for around 5 minutes until softened.
Add the mustard powder, ground coriander, cumin, turmeric, black pepper, chilli flakes and asafoetida, if using. Stir in the ginger and, if using, the minced garlic. Cook for around 1 minute until fragrant.
Add the diced sweet potato and stir well to coat it in the spices.
Pour in the coconut milk and vegetable stock and stir everything together.
Bring to a gentle simmer and cook for around 20-25 minutes, stirring occasionally, until the sweet potato is tender but still holding its shape.
Add the drained chickpeas and simmer for another 5-10 minutes.
Stir through the frozen peas and cook for another 3-4 minutes until heated through.
Taste and adjust the seasoning, then add a squeeze of lime or lemon juice if you like.
Finish with fresh coriander and, if using, a scattering of toasted flaked almonds. Serve with rice or your favourite accompaniment.
Tip: I particularly like using white-fleshed sweet potato in this curry because it stays slightly firmer in the sauce, but regular orange sweet potato works just as well.