Pat the ahi tuna steak completely dry with paper towels and season both sides with sea salt and black pepper.
Heat a non-stick skillet over high heat and add half of the toasted sesame oil.
Once the pan is smoking slightly, sear the tuna for exactly 60 seconds per side to achieve a golden crust while keeping the center rare.
Remove the tuna from the pan and let it rest for 2 minutes before slicing into half-inch cubes.
In a small bowl, whisk together the tamari, rice vinegar, and the remaining sesame oil to create the dressing.
Place the cooked white rice in the center of a bowl and arrange the sliced cucumber, edamame, sliced radishes, and avocado around the edges.
Top the rice with the seared tuna cubes, drizzle the dressing over the entire bowl, and garnish with sesame seeds and torn nori pieces.