In a large saucepan, heat the oil over medium heat. Add the cumin and toast for about a minute, until fragrant and lightly darkened in color (be careful not to burn them). Immediately stir in the onion and cook until the onion is soft and translucent.
Add the garlic, ginger, turmeric and coriander. Stir to combine and cook until the garlic softens.
Add the sweet potato, chickpeas, tomatoes with their juices and coconut milk.. Cover and simmer over medium heat until the potatoes are fork-tender.
Stir in the spinach and cook until wilted. Add chilli to taste. Season with the salt and black pepper.
Serve on a bed of cooked rice with fresh chopped cilantro . If desired, offer lime wedges over the curry. You can store curry in an airtight container in the fridge for 4 to 5 days.