Spicy tuna and fresh, cool vegetables wrapped up in one rice paper round.
Sauce: In small bowl, whisk ponzu, sesame oil, and sesame seeds.
Soak It: Fill a large dish with lukewarm water. (A pie plate works well.) Add 1 rice paper round and let soak, turning often, just until barely pliable, 5 to 10 seconds. You’re going to think that it’s not soft enough, but trust us: If you let it get too soft, it will get super sticky and be near impossible to roll.
Roll It: Transfer the rice paper round to a damp work surface. In medium bowl, whisk mayonnaise and sriracha. Fold in tuna. Across top half of each rice paper round, arrange one-quarter of cucumber. Across each bottom half, arrange one-quarter of tuna, scallions, and avocado. (The ingredients across the top half of the rice paper will end up in the top half of the roll, which will make your rolls look extra pretty.) Fold the bottom edge of the rice paper over the filling. Fold in the sides, then roll it up like a burrito. Repeat the soaking, filling, and rolling with the remaining ingredients. Serve with the sauce.