For the lentils: put the cooked and drained lentils in a bowl. Then add in some spring onions, capers, gherkins, chives and parsley, to taste. Dress with mustard, black pepper, salt and olive oil. Set aside.
For the tartar sauce: put some mayonnaise in a bowl. Then add in some spring onions, capers, gherkins, chives and parsley, to taste. 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, roll the salmon and filling 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 slice the delicate roll into pieces, like a Japanese Maki or sushi roll. Serve immediately.