Boil buckwheat: Fill a saucepan with water, put it on a cooker, add buckwheat(if you change the ammount of buckwheat, be sure to change the ammount of water. It's always 1:2 - buckwheat : water), wait till it's bubbled, add salt and put a lid on a sausepan, make the fire on minimum and let it boil for 15-20 minutes(depends on buckwheat).
Chicken preparation: Cut chicken brests into thin stripes, dice an onion into small pieses, pour 1 tbsp of oil (sunflower/olive) into a pan, add diced onion and saute it till it starts getting golden colour, add chicken breast stripes and a little of water, put a lid on a pan. Make sure there is enough water in a pan not to let chicken breast to be fried.
Adding sauce for chicken: when the chicken is cooking in a pan, take a glass or a cup, pour a tbsp of water, 3 tbsp of sour cream, salt and pepper, mix it together. Look if the chicken stripes have no raw view, add the mixture from the cup to chicken (make sure there is still some water in a pan, if there is no water, add some), stir it all, add flour and stir once again. The sause should start thickening. 10 min later make the cooker off (do not let the sause and chicken be fried).
Adding all together: now when buckweat and chicken are ready it's time to mix it together. Some prefer mixing it all and then make portions, I prefer to put buckwheat on plate and on top pour sause with chicken stripes. Now it's time to enjoy your meal!