Cook the brown rice according to package instructions and set aside to cool slightly.
Pat the sushi-grade ahi tuna dry with a paper towel and cut into even 1-inch cubes.
In a medium glass bowl, whisk together the tamari, sesame oil, rice vinegar, grated fresh ginger, sea salt, and black pepper.
Add the tuna cubes to the dressing and toss gently to coat, then let it marinate in the refrigerator for 10 minutes.
While the tuna marinates, slice the cucumber into thin rounds and pit and slice the avocado.
Steam the shelled edamame until tender and bright green.
Assemble the bowl by placing the brown rice at the base and topping with the marinated tuna, cucumber, edamame, and avocado.
Garnish with sesame seeds before serving.