Add the tuna to a medium mixing bowl and toss together with the soy sauce, green onions, sesame oil, sesame seeds, and hot pepper until well combined.
In another small bowl, toss together the cucumbers, radishes, rice vinegar, and salt until well combined.
Divide the rice evenly among four bowls. Top with tuna, cucumber/radish mixture, mango, and avocado in sections. Garnish with sauce (if desired) and serve.
Notes
For extra flavor, you can follow step one and then marinate the tuna for before serving.