In a small bowl mix cream cheese and dill together.Add lemon juice, season to taste with salt and pepper.
Using a rolling-pin, gently flatten each slice of bread - if you are able to purchase extra thin bread rolling may not be necessary.
Working on a flat surface, take 10 slices of the flattened white bread and 5 slices of whole wheat bread and spread with a thin layer of the cream cheese mixture.
Top 5 slices of white bread with smoked salmon, then top with a slice of whole wheat bread, cream cheese side up. Top the 5 sandwiches with red onions and top with white bread cream cheese side down.
Using a serrated knife cut off the crust on all four sides. Slice into quarters on the diagonal and serve.