Put a tawa or a pan over medium flame and add flax seeds on it. Roast the seeds over medium flame and stir in between so that they don't burn.
Peel and roughly chop the raw mangoes and add to a blender jar. Next, add all the remaining ingredients except mustard oil and jaggery to it and pulse to a fine paste.
Transfer to a bowl and add jaggery powder to it. Pour mustard oil in the last and mix well and your chutney is ready to serve. Enjoy with Dal Rice or Sabji Roti.