Put the lentils in a bowl. Then add in half the gherkins, capers, chives, parsley and spring onions. Dress with the olive oil, mustard and salt and pepper to taste. Set aside.
Put the mayonnaise in a bowl. Then add in the remaining half gherkins, capers, chives, parsley and spring onions. Set aside.
Lay some plastic wrap on a cutting board, which will help to form the roll. Start to layer the sheets of smoked salmon on top, overlapping the slices, so that none of the filling escapes when you roll it up.
Using an offset spatula (commonly used for frosting cakes), spread a thin layer of the tartar sauce right on the salmon, all the way to the outer edges of the salmon. Next, spoon on a layer of the prepared lentils over the tartar sauce layer.
Using the plastic wrap to help, lift the salmon away from you and form it into a log form. (The plastic wrap helps to lift the delicate salmon. The plastic wrap should not get rolled into the salmon.) Once the roll is formed, use a very sharp knife to very gently slice the delicate roll into pieces, like a Japanese maki or sushi roll. Serve immediately on individual spoons or on top warm toasted baguette slices drizzled with a little olive oil.
Cook's Note: The success of this final dish is dependent on using the best quality smoked salmon and ingredients.