Whisk together the soy sauce, garlic, honey, sriracha and sesame oil. Pour into a heavy-duty zip top bag or shallow dish, add the steak and turn several times to coat. Marinate for at least 4 hours, turning occasionally.
Preheat a grill, grill pan or broiler on high heat. While the grill preheats, prepare the mushrooms. Heat the sesame oil in a wok or skillet over medium-high heat. Add the garlic and ginger and stir-fry until fragrant and soft, 2 minutes. Add the mushrooms and continue cooking until any liquid they've given off has evaporated and they begin to brown. Add the soy sauce and mirin and simmer until the liquid has reduced slightly and the mushrooms are tender, 3 minutes. Add the scallions and remove from the heat.
Cook the steak for 2-1/2 to 3 minutes per side for rare to medium-rare. Allow to rest for 5 to 7 minutes before slicing across the grain. Serve with steamed rice and top with the mushroom-scallion mixture.