In a medium mixing bowl, combine the drained tuna, mayonaise, cream cheese, olive oil, chopped spring onions and lime juice. Once fully combined, use a stick blender to puree until mostly smooth (this will help to spread the mixture evenly on the nori sheet).
Finely slice your cucumbers (length ways), and your avocado, and set aside.
Lay out a nori sheet (rough side up) on a wooden cutting board, and with a wide butter knife or spatula, thinly spread over a layer of the tuna mix, leaving a thin rim at the start (you want a little space to get the roll started) and 1/5th at the other end. Take your time to get a nice even, and thin, layer of the tuna mixture, getting right to the edges, but leaving space at the end.
Lay multi slices of the cucumbers together, lengthways, at one end of the sheet, then lay the avocado slices next to the cucumber.
Take the edge of the nori sheet and roll tightly over the cucumbers and avocado, then continue to roll. To seal it at the end, dab a bit of water on the very edge of the nori sheet.
Using a very sharp knife, slice your roll into pieces using a saw-ing motion. Try not to put pressure on the roll otherwise the filling will spill out. Repeat again, and you should have about 14-15 pieces.