Spicy Tuna Hand Rolls

Name: Spicy Tuna Hand Rolls
Ingredients: 1 1/4 cups sushi rice, rinsed; 1 tablespoon unseasoned rice vinegar; 1 tablespoon sugar; Kosher salt; 2 tablespoons sesame seeds, toasted; 2/3 cup mayonnaise; 2 tablespoons fresh lemon juice; 3 to 4 teaspoons Sriracha; 1 tablespoon soy sauce; 1 teaspoon sesame oil; 1 teaspoon grated peeled ginger; 3/4 pound ahi tuna (about 1 1/4 inches thick); Kosher salt and freshly ground pepper; 1 tablespoon vegetable oil; 6 sheets nori; 1 avocado, thinly sliced; 1 cucumber, cut into matchsticks; 1 carrot, cut into matchsticks; 1/2 bunch chives, cut into 3-inch pieces; Pickled ginger, for serving (optional)