In a pan, dry roast the cumin seeds, fennel seeds, fenugreek seeds, carom seeds, and mustard seeds. Let them cool down to room temperature.
Transfer them into a blender and grind into a fine powder. Keep aside.
Next, take the chopped red chilies in a mixing bowl. Add the prepared spice mix followed by the turmeric powder, red chili powder, nigella seeds, and salt and mix.
Add the mustard oil next and mix well.
Transfer the chilies into a glass container and let it sit for at least 5 hours before consumption.
Store in the refrigerator and eat a few pieces along with your meal.