While water comes to boil, stack spinach leaves, roll into a tight tube lengthwise, and cut crosswise into thin shreds. Heat remaining 1 tablespoon sesame oil in a large skillet over medium-high heat, and cook scallions and mushrooms until tender and lightly browned, about 5 minutes. Add ginger and garlic; stir for 1 minute. Add spinach, broth, remaining tamari, remaining honey, Sriracha, and toasted sesame oil, and cook for 1–2 minutes, until spinach is just wilted. Season to taste with black pepper and additional tamari, if needed.