Spicy Tuna Roll

Name: Spicy Tuna Roll
Prep time: 30 min
Total time: 30 min
Cuisine: American, Japanese
Ingredients: 2 Persian cucumbers, peeled and julienned; 1/2 tsp. rice wine vinegar; 1/4 tsp. kosher salt; 2 (5-oz.) cans tuna packed in water, drained; 1/4 c. mayonnaise (preferably Kewpie); 3 tbsp. Sriracha; 1 tsp. togarashi (optional); 6 nori sheets; 4 c. prepared sushi rice, divided; 1 avocado, sliced 1/3" thick; Black and white sesame seeds and thinly sliced scallions, for garnish