Place all ingredients except the herbs, onion and sesame seeds into a food processor and process into a paste. You can add water in very small increments if it needs binding. Transfer to a mixing bowl. Stir in herbs, onion and sesame seeds. Mix well. Will keep in the refrigerator for 5 days.
To assemblePlace a nori sheet siny side down on rolling mat or chopping board. Place a large flat piece of cabbage onto nori sheet so the edge of the cabbage is at the end of the nori sheet closest to you and covers the length of the nori sheet. Spread out walnut tuna mix right to the ends, make approximately 1 inch thick. Then add your sliced cucumber, dash of wasabi, tamari, lemon juice, sliced avocado, sprouts and coriander. Spread out along the length of the sushi roll.Then carefully start rolling the sushi roll away from you, keeping pressure on so the contents remain tightly enclosed. Once you have completed the roll, leave about an inch of the nori sheet spare at the end and dab with water to moisten. Then roll to seal and slice with a sharp knife into bite sized pieces. Serve.
