Cook the white rice according to package instructions and set aside to cool slightly.
Pat the ahi tuna dry with a paper towel and cut into 1/2-inch uniform cubes.
In a medium glass bowl, whisk together the tamari, toasted sesame oil, rice vinegar, and freshly grated ginger.
Add the tuna cubes to the bowl and toss gently to coat; let marinate in the refrigerator for 10 minutes.
Prepare the vegetables by thinly slicing the cucumber and radishes, and dicing the avocado.
Place the cooked rice in a serving bowl and arrange the marinated tuna, edamame, cucumber, radishes, and avocado on top.
Garnish with sliced green onions, sesame seeds, and strips of nori seaweed before serving.