Slice the mushrooms. Mince the garlic. In a small bowl, stir together the garlic with the tamari, mirin and Sriracha.
Heat the sesame oil in a pan over medium-high heat. Add the mushrooms and cook 3 to 4 minutes, turning occasionally as they start to brown. Add a few pinches of kosher salt while cooking. Pour in the bowl of sauce and continue cooking 1 to 2 minutes until browned and glossy.