Pat the ahi tuna dry with a paper towel and cut into uniform 1/2-inch cubes.
In a small glass bowl, whisk together the tamari, toasted sesame oil, rice vinegar, and freshly grated ginger.
Add the tuna cubes to the marinade, tossing gently to coat, and let rest in the refrigerator for 10 minutes.
Prepare the tropical salsa by combining the diced mango, finely diced red onion, chopped cilantro, and lime juice in a separate bowl.
Place the warm cooked brown rice in the center of a serving bowl.
Arrange the marinated tuna, mango salsa, sliced avocado, shelled edamame, and sliced cucumber in sections over the rice.
Garnish the entire bowl with black sesame seeds and serve immediately while the tuna is chilled.