Heat the oil in a pan over medium heat. Add the cumin seeds (if using), garlic, green chilies, cilantro stems, and salt. Sauté for 2 minutes.
Add the peanuts and sauté for 2 to 3 minutes until the garlic starts getting light golden marks.
Turn the heat off and let the mixture cool completely.
Crush in a mortar and pestle (in batches), or pulse in a spice blender or food processor, until you reach the texture you want. Traditional thecha is coarse. For thecha paneer, grind it finer. Pulse the blender in short bursts for that perfect texture.
Add the lemon juice and give one good mix to the thecha.
Lavangi mirchi are quite spicy, and thick green chilies are milder. Together, they give the best flavor and heat.