1. Season tuna steak generously with salt and pepper. Place sesame seeds on a shallow plate and press tuna steak into seeds until fully coated on all sides. Preheat skillet until very hot, then sear tuna for about 45 to 60 seconds on each side. Set aside. (Note: Tuna can be seared a day in advance. Let cool, cover, and refrigerate.)
2. Bring a large pot of water to a boil. Carefully add eggs and set a timer for exactly six and a half minutes. When eggs are done, remove with a slotted spoon and place straight into an ice bath to stop cooking.
3. Add green beans to boiling water and cook for exactly three minutes. Drain and add green beans to ice bath to stop cooking.
4. To make herb dressing, combine all ingredients and let sit for at least 10 minutes. (Note: Herb dressing can be made a day in advance.)
5. Spread arugula on a large platter or on individual plates. Top with sliced tuna, halved eggs, green beans and a drizzle of herb dressing.