Heat the olive oil in a skillet over medium heat; fry the chana dal, mustard seeds, and asafoetida powder in the hot oil until the mustard seeds pop and the chana dal turns golden brown, 2 to 3 minutes. Stir the tomatoes and green chile pepper into the mixture; cook until the tomatoes are tender, about 7 minutes.
Remove from heat and allow to cool for a few minutes; stir the yogurt and salt into the mixture.