Bring the lentils to boil. They will take around 45 minutes, so reserve some time for it.
Meanwhile, cut the champignons and bell pepper in small pieces and fry them in a frying pan.
When the lentils are ready, blend half of them together with half of the champignons and pepper, olive oil and tamari. Blend till you get a porridge-like mass.
Transfer the mixture to a bowl, add the rest of the lentils and part of the veggies (you can leave the rest of the veggies for decoration, or add them), and knead/mash.
Add some buckwheat flour. The quantity will depend on how wet the mixture is, so you might need to use less or more of it. The end result needs to be a dough-like mixture that you can easily roll nice balls from.
Form the mixture into balls with your hands and flatten these with your hand to form burgers. Fry them on a reasonably high fire in a bit of olive oil on both sides.