Heat the oil in a large non-stick pan. Sauté the onions on high heat until golden, then add the tomatoes. Under regular stirring cook the mixture until it turns into a thick paste.
Add some salt and the turmeric powder. After a minute throw in the potatoes and approx. 50 milliliters water. Covered and on low heat, simmer the potatoes until soft and the water has evaporated – this takes about 15-20 minutes.
Stir in the mango pickle sauce and a sprinkling of pepper. Garnish with the chopped coriander leaves and serve with warm rotis or pita bread