In a large pan over medium heat, warm up the 2 tbsp of Olive Oil. Once hot, add the cumin seeds and mustard seeds.
Once the spices start popping, add ginger, garlic and onion. Sauté until onion has softened and is beginning to turn translucent.
Add the remaining spices - turmeric, garam masala, ground coriander and chilli powder - to the mixture and cook for 1-2 minutes, or until fragrant.
To this spicy onion mix, add the diced mango cubes, mixing everything together well. Cook for about 5 minutes when the mango should be starting to soften.
Pour in the coconut milk and bring everything to the boil. Turn the heat down to low and allow to simmer away for 20 minutes at which point the sauce should have thickened slightly and your mango should be very soft.
Using an immersion blender, blitz everything together to a pulp until there are no lumps of mango or onion left. Taste the sauce and season as desired with salt and pepper.
If your mango wasn't very sweet, you may also want to balance the sauce out with a 1 or 2 tsp of light brown sugar. This is completely optional though.
To the sauce, add the chickpeas, spinach and coriander leaves. Combine everything together well and allow the spinach to wilt completely.
If you want your sauce slightly less thick, add the optional 1/4 cup of non-dairy milk to loosen slightly.
Serve up with some fresh coriander leaves and a bed of rice!