In a bowl, stir together the Nashi, sugar, soy sauce, sesame oil, garlic, ginger, salt and pepper to taste and stir until the sugar has dissolved. Add the beef, coating in the marinade and then cover and allow to marinate in the fridge for at least 2 hours.
Preheat charcoal grill over medium-high heat until very hot. Brush grills with vegetable oil. Remove steaks from marinade, wipe and place on the grill. Cook on each one side for about 5 minutes. Should be medium rare, then remove and hold in a warm place for 10 minutes to rest.
Slice the steaks on a cutting board. Pile on a big plate with the lettuce leaves, shredded onion and serve with a bowl of rice and Sriracha sauce. Place meat in a lettuce cup, add rice, spring onions and coriander, drizzle with sauce, wrap and eat.