Cut the ahi tuna into 1 inch cubes cutting against the grain. Transfer the tuna to a medium size bowl. Add green onions, serrano pepper, fresh ginger, cucumber and salt to the tuna.
In a small bowl, whisk together coconut aminos, fish sauce, macadamia nut oil and garlic. Add the coconut aminos mixture to the tuna.
Fold in the sesame seeds and macadamia nuts. Cover and refrigerate for at least 2 hours.
Add sea salt to taste and fresh lime juice, right before serving.