In a medium bowl, whisk together soy sauce, brown sugar, green onions, garlic, sesame oil, ginger, pear and Sriracha, if using. Reserve 1/4 cup and set aside.

In a gallon size Ziploc bag or large bowl, combine soy sauce mixture and steak; marinate for at least 1 hour to overnight, turning the bag occasionally. Drain the steak from the marinade.

In a large saucepan of 2 cups water, cook rice according to package instructions; set aside.

Preheat grill to medium high heat. Add steak to grill and cook, flipping once and basting with reserved 1/4 cup marinade until cooked through, about 1-2 minutes on each side.

To serve, spoon rice into the center of a lettuce leaf, taco-style; top with steak, garnished with sesame seeds, if desired.