Cook the brown rice according to package instructions and set aside to cool slightly.
In a medium glass bowl, whisk together the tamari, sesame oil, lime juice, and freshly grated ginger.
Pat the ahi tuna dry with a paper towel and cut into 1/2-inch uniform cubes.
Place the tuna cubes into the marinade, tossing gently to coat, and let sit in the refrigerator for 10 minutes.
Prepare the vegetables by slicing the cucumber into half-moons, thinly slicing the radishes, and dicing the avocado.
Place the cooked brown rice in the bottom of a serving bowl.
Arrange the marinated tuna, edamame, cucumber, radishes, and avocado on top of the rice base.
Garnish with sliced green onions, sesame seeds, sea salt, and black pepper before serving immediately.