Heat the oil in a heavy pot. Add the onion and sauté until soft, then add the garlic and sauté for about 40 seconds. Add the shado beni and cook, stirring, for 30 seconds.
Add the turmeric, curry powder, and amchur masala, and cook for 30 seconds.
Add the mangoes and sugar, and stir well to coat. Add enough water to barely cover the mangoes, and mix well