Heat olive oil in a large skillet under medium high heat. Season tuna with salt and pepper. Add to skillet and cook for 2-3 minutes per side. If you want a nice medium rare, I'd go a little under 2 minutes. As you can see from the picture above, I went a little over and got a small margin of rarity. Let tuna rest on cutting board for 5 minutes.
Meanwhile, add the haricots verts to the boiling water and cook until tender, about 3-5 minutes. Drain.
In a small bowl, mix together the lime juice, lime zest, garlic, and wasabi. You may have to add a little water also if there's not enough liquid. Add mixture to the haricot verts, along with the scallions.
Thinly slice tuna and serve with haricot verts. Top with black sesame seeds!