Seared Tuna Salad with Wasabi Butter Sauce

Mix panko and sesame seeds on a large plate or shallow bowl. Season tuna with salt and pepper, to taste. Gently press both sides of each tuna steak into the crumb mixture. Heat a large skillet over medium-high heat and spray with oil. Add 2 steaks, spray each with oil and allow them to cook 2-3 minutes, or until the outer edge becomes opaque. Flip each steak, spray second side with oil and cook an additional 2 minutes, or until the outer edge is opaque. Repeat with remaining 2 steaks. Set all 4 steaks on a cutting board and allow them to rest and cool. Meanwhile, in a small bowl, combine soy sauce and wasabi paste. Set aside. In a small skillet over medium-low heat, add shallots and wine. Simmer until reduced by half, 2-3 minutes. Add the milk and whisk constantly until the sauce no longer looks separated and has slightly thickened (about 1 minute). Remove from heat and whisk in soy and wasabi paste mixture. Add butter and whisk to combine. To serve: Distribute arugula and spinach evenly among 4 shallow bowls. Thinly slice the tuna and top each bed of lettuce with 1 tuna steak. Drizzle each with about 1 ½ tablespoons of sauce. Serve immediately.