In a gallon sized ziplock bag, add the soy sauce, lime juice, sesame oil, and ginger.
Add the tuna steaks to the bag and marinate for at least 3 hours.
When ready to cook, pour the sesame seeds onto a plate. Remove the tuna steaks from the bag and brush with the tahini.
Coat the tuna steaks on all sides with the sesame seeds.
Add the Grapeseed oil (enough to coat the entire bottom of the pan). Heat grapeseed oil in a medium non-stick pan over medium heat for 3 minutes. Do not let the oil get hot to the point where it starts smoking or it will burn the sesame seeds before cooking the fish.
Cook for 2-3 minutes, tilting the pan and using a spoon to redistribute the oil on top of the fish as it cooks. Flip and cook 2 minutes.
Prepare your salad base using any salad greens - spinach, field mix, whatever you prefer. Add whatever salad toppings you like - tomatoes, toasted cashews, avocado, cucumbers, etc. This is especially tasty with a sesame ginger salad dressing.