Cook the brown rice according to package instructions and set aside to cool slightly.
Pat the sushi-grade yellowfin tuna dry with a paper towel and cut into even 1/2-inch cubes.
In a medium glass bowl, whisk together the coconut aminos, toasted sesame oil, grated fresh ginger, lime juice, and sriracha.
Gently fold the tuna cubes into the marinade, ensuring every piece is coated, and let it marinate for 5 to 10 minutes.
While the tuna marinates, thinly slice the cucumber, radishes, and green onion, and dice the avocado.
Assemble the bowl by placing the brown rice at the bottom, then topping with the marinated tuna, edamame, cucumber, radishes, and avocado.
Drizzle any remaining marinade over the bowl and garnish with black sesame seeds and sliced green onions.