Heat the oil in a large saucepan over a low-medium heat. Tip in the onion and chilli and cook slowly for 10-12 minutes, stirring occasionally, until soft. Add the ginger garlic paste and dried spices and cook for a few more minutes, stirring often.
Add the tomatoes and cook for 2 minutes, then add the cooked beetroot and coconut milk and simmer for 15 minutes. Stir in the tamarind, spinach and half of the chopped coriander and simmer for a final 5 minutes.
Divide among bowls and sprinkle over the remaining coriander. Serve with wedges of lime on the side (if using) and rice or flatbreads.