Season the ahi tuna steak evenly with sea salt and black pepper on both sides.
Heat the sesame oil in a heavy-bottomed cast-iron skillet over high heat until it begins to shimmer.
Carefully place the tuna in the skillet and sear for exactly 1 minute per side to achieve a golden crust with a rare center.
Remove the tuna from the pan and let it rest on a cutting board for 2 minutes before slicing into thin strips against the grain.
In a small mixing bowl, whisk together the tamari, rice vinegar, and ground ginger until well combined.
Place the warm cooked brown rice in the center of a serving bowl.
Arrange the sliced tuna, edamame, cucumber, radishes, and avocado over the rice in distinct sections.
Drizzle the prepared ginger-tamari dressing over the entire bowl and garnish with sesame seeds.