Heat 1 teaspoon oil in a pan over medium heat. Add the mint leaves and fry until slightly wilted, 3 to 5 minutes. Remove from heat and set aside.
Heat 2 teaspoons oil in a frypan (or a kadhai if you have one). Add the red chillies, black lentils, coriander seed, chana dal and mustard seed; cook in the hot oil until the lentils brown and the seeds start to splatter; remove from heat and allow to cool slightly. Grind the mixture into a coarse powder using a mortar and pestle; add the mint leaves, tamarind paste and salt; continue crushing until the mint is completely integrated.