Pat the ahi tuna dry with a paper towel and cut into 1/2-inch cubes using a sharp knife.
In a medium bowl, whisk together the tamari, toasted sesame oil, rice vinegar, grated ginger, sea salt, and black pepper.
Add the tuna cubes to the marinade, tossing gently to coat, and let sit in the refrigerator for 10 minutes.
In a small separate bowl, combine the diced mango, chopped green onion, and lime juice to create the tropical salsa.
Place the cooked brown rice in the base of a serving bowl.
Top the rice with the marinated tuna, edamame, sliced cucumber, and avocado slices.
Garnish the bowl with sesame seeds and any remaining green onions before serving immediately.