Remove the stem of chilles, slit them open and then remove the seeds.
Next in a grinder add mustard seeds, fenugreek seeds, nigella seeds, fennel seeds grind to make a coarse powder.
Transfer the masala in a bowl.
Now in the same bowl add asafoetida, red chilli powder, turmeric powder, coriander powder, dry mango powder and salt.
Mix well and add oil in it little at a time while mixing it to make a thick paste.
Now stuff chillies with generous amount of masala in it.
Now heat 1 tbsp mustard oil in a pan.
Once oil is warm add chillies in it and spread chillies in single layer.
Cover and cook on medium high for 2-3 minutes.
After 2 minutes flip them over turn off the heat and let it cook from both the sides.