Prepare the brown rice according to package directions and set aside to cool to room temperature.
Using a sharp chef's knife, carefully dice the sushi-grade ahi tuna into uniform half-inch cubes.
In a medium glass bowl, whisk together the tamari, toasted sesame oil, freshly grated ginger, and lime juice until emulsified.
Add the diced tuna to the bowl, tossing gently to ensure every piece is coated in the zesty marinade, then chill for 10 minutes.
Prepare the toppings by slicing the cucumber into thin half-moons, julienning the radishes, and dicing the avocado into small chunks.
Build the bowl by placing the cooled rice at the bottom and arranging the marinated tuna, edamame, cucumber, radishes, and avocado on top.
Finish the dish by sprinkling with black sesame seeds and thinly sliced green onions for a vibrant, clean-eating meal.