Spread the raw peanuts on a plate and pick out any shriveled or discolored ones, then pat them dry with a clean towel if they feel damp.

Add the peanuts to a dry kadai over medium-low heat and roast, stirring constantly, until the skins darken slightly and the peanuts smell nutty and toasted.

Transfer the roasted peanuts to a wide plate and let them cool completely so they turn crisp instead of staying chewy.

Heat the oil in the same kadai over medium heat and add the mustard seeds, letting them sputter and pop.

Add the curry leaves, chopped garlic, and slit green chilies to the hot oil and sauté briefly until the garlic turns light golden and the leaves crisp up.

Lower the heat and stir in the red chili powder, turmeric, and asafoetida, mixing quickly so the spices bloom in the oil without burning.

Tip the cooled roasted peanuts into the kadai along with the salt, and toss everything together so the peanuts are evenly coated in the tempered spice oil.

Keep tossing the peanuts over low heat until the spice mix clings evenly to every peanut and no dry powder remains at the bottom of the pan.

Turn off the heat, squeeze the lemon juice over the peanuts, toss once more, and let them cool completely before serving or storing.