Pat the ahi tuna dry with a paper towel and cut into half-inch cubes using a sharp knife.
In a medium glass bowl, whisk together the tamari, toasted sesame oil, lime juice, grated fresh ginger, sea salt, and black pepper.
Add the cubed tuna to the dressing and toss gently to coat, then let it marinate in the refrigerator for 10 minutes.
While the tuna marinates, lightly steam the cauliflower rice in a pan with a splash of water until tender but still firm.
Slice the cucumber into thin half-moons and dice the avocado into small chunks.
Place the warm cauliflower rice at the base of a bowl and top with the marinated tuna, edamame, cucumber, and avocado.
Garnish the bowl with sliced scallions and sesame seeds before serving immediately.