Tuna Sushi Burrito

Name: Tuna Sushi Burrito
Ingredients: 1 1/2 cups short-grain white rice; 2 tablespoons granulated sugar; Kosher salt and freshly ground black pepper; 6 tablespoons unseasoned rice wine vinegar; 1/2 cup mayonnaise, preferably Japanese style; Three 5-ounce cans tuna in water, well drained; 2 scallions, white and light green parts only, thinly sliced; 8 roasted nori sheets (about 8 inches square); 1/4 cup furikake rice seasoning (see Cook's Note); 1/2 medium carrot, peeled and cut into matchsticks; 1/2 English cucumber, seeded and cut into matchsticks; 1/2 medium red bell pepper, thinly sliced; 1/2 large ripe avocado, thinly sliced