Prepare the brown rice according to package instructions and set aside to cool slightly.
Slice the sashimi-grade ahi tuna into 1/2-inch uniform cubes using a sharp knife.
In a medium glass bowl, whisk together the tamari, toasted sesame oil, rice vinegar, grated fresh ginger, and sea salt.
Add the tuna cubes to the marinade and gently toss to coat, then let it sit in the refrigerator for 10 minutes.
Thinly slice the cucumber, shred the carrots, and shell the edamame if they are in pods.
Layer the cooked brown rice at the bottom of a bowl and top with the marinated tuna, cucumber, carrots, and edamame.
Garnish with sliced avocado, chopped green onion, and a sprinkle of black sesame seeds before serving.