Spread the sushi rice over the nori sheet to cover evenly, leaving a 1½ cm margin on the side furthest from you. Spread the rice to smooth the surface, but do not press it down too hard. Spread a little wasabi paste, to taste, across the rice.
Prepare the fillings in separate bowls and spread/ arrange horizontally in a row along the centre – eg make one section with salmon and red pepper and the other with tuna mayonnaise and shiso leaves - and allow them to poke out of the sheet slightly. Hold the sushi mat with both hands and carefully roll up, neatly wrapping the different fillings in the middle while rolling away from the side closest to you. When rolled, hold the sushi mat with both hands and squeeze gently to firm up the roll.
Leave the roll on the work surface for at least 5 minutes with the nori joining side touching the work surface – this should enable the nori to stick naturally (you shouldn’t need to add water to help it stick).
Using a sharp knife, slice the sushi into pieces and serve.