Sushi Rice: Rinse sushi rice with water, untill water runs clear. Combine water and seasoned vinegar in a pot over medium high heat, bring to a boil. Add the sushi rice; stir and bring to a boil. Reduce heat to simmer, cover and cook 15 minutes. Once rice is cooked remove from heat and set aside.
Poke with Avocado: Whisk together the soy sauce, sesame oil, vinegar, sesame seeds and crushed red pepper in a medium mixing bowl. Add the cubed tuna and scallions, gently stir together to dress the tuna. Marinate 10 to 12 minutes.
Meanwhile, pit and cube the avocado (the chunks should be similar size to the tuna). Add to the tuna, and gently mix together to distribute the avocado.
To serve, scoop rice into bowls making a mound, top with mound of Tuna Poke, garnish with additional scallions and white and black sesame seeds.