In a large skillet over medium heat, heat the ghee.
Season tuna with salt and pepper. Sear fish in the skillet for 2 to 4 minutes on each side, until tuna is cooked to desired level of doneness. Remove and allow to cool then slice.
In a large bowl, toss the tuna with the lettuce, onion, radish, kale and celery.
In a medium bowl, whisk the remaining ingredients with sea salt and freshly ground black pepper to taste. Pour the dressing over the salad, toss and serve.