Prepare the brown rice according to package instructions and allow it to cool slightly to room temperature.
Pat the sushi-grade ahi tuna dry with a paper towel and cut into uniform 1/2-inch cubes.
In a medium glass bowl, whisk together the tamari, sesame oil, lime juice, rice vinegar, and sriracha until emulsified.
Add the tuna cubes to the marinade, tossing gently to coat, and let it marinate in the refrigerator for 5 to 10 minutes.
Thinly slice the cucumber and radishes, and dice the avocado into small chunks.
Place the cooked brown rice in the center of a serving bowl.
Top the rice with the marinated tuna and arrange the edamame, cucumber slices, radishes, and avocado around the perimeter.
Garnish the bowl with thinly sliced green onions, sesame seeds, sea salt, and black pepper before serving.