Rinse the lentils cold and boil them in the broth. Leave to swell over low heat for about 7 minutes. Wash cucumber thoroughly and rub dry. Cut or slice into thin slices. Mix oil, lemon juice and mustard well together.
Wash the dill, dab dry and chop. Add to the sauce. Season to taste with salt, pepper and sugar. Mix cucumber and lentils with the mustard sauce. Arrange each with two slices of salmon on a plate