Heat peanut oil, let it come to a warm temperature then keep aside. Take split mustard seeds in a blender jar and grind them until coarse powder.
Mix crushed seeds and warm oil to a big bowl. Now add lemon juice and mix everything again. Keep this aside for about 4 to 5 hours.
Wash and completely dry the chili peppers. Cut the top then cut lengthwise and put in a big bowl. Add turmeric powder and salt. Mix well.
Cover the bowl and keep aside for an hour. With the help of a perforated ladle, spread in a single layer on a paper towel. Discard the water. Let it air dry for about 5 to 6 hours.
Once the chilies are dried, take them into a big bowl. Add in the Mustard-fenugreek mixture and mix everything very well.