Chop the onion, carrot, and celery into small pieces. Put them pot with a little water and cook.
Add the buckwheat, lentils (after draining the soaking water) and water equal to about three times the volume of buckwheat and lentils. Add salt to taste.
Bring to boil then lower the heat. Cook for about 25 minutes. Once all the water has been absorbed, turn off the heat, leave for 5 minutes and serve with the oil and chopped parsley.