Place the tuna steak in a wide bowl, and add the coconut aminos, ginger, and garlic. Cover with plastic wrap. Marinade refrigerated for 15 minutes. Flip the steak, spoon the marinade over it, recover, and marinade another 15 minutes. For the second half of the marinade, you can allow to come up to temperature (not refrigerated).
Prepare the vegetables: Spiralize the cucumber, thinly slice the bell pepper, julienne the carrot.
Preheat your grill to high heat. (At least 450 F).
Bring together the Sesame Ginger Dressing ingredients. Whisk together, and set aside.
Plate the salad greens, adding the carrot, cucumber, and bell pepper. Slice the avocado (doing this earlier risks it getting oxidized). Add the avocado to the salad plates.
Grill the tuna steaks on high heat for about 4 minutes per side (for rare tuna). Pour the remaining marinade over the tuna after you've flipped it.
Allow the tuna to rest for 5 minutes, then slice into 1/4" pieces. Plate in the center of the salad bowls, and dress everything with the sesame ginger dressing.
Garnish with thinly sliced green onions, and serve.