Place the raw mangoes in ice-cold water for atleast 30 minutes and drain. Keep aside.
Combine the sugar, red chillies, tamarind pulp and lemon juice and grind in a mortar-pestle (khalbhatta) till the mixture is coarse. Keep this dressing aside.
Combine the mangoes, brown sugar-chilli dressing, tomatoes and salt into a bowl and toss gently.