In a medium bowl, whisk together the coconut aminos, toasted sesame oil, grated Asian pear, minced garlic, grated ginger, and black pepper to create the marinade.
Add the thinly sliced beef sirloin to the bowl, tossing thoroughly to ensure every piece is coated, and allow it to marinate for at least 15 minutes.
Heat a large cast-iron skillet or wok over high heat until it begins to smoke slightly.
Add the marinated beef to the skillet in a single layer, searing for 1-2 minutes per side until deeply caramelized and cooked through, then remove the beef and set it aside.
In the same skillet, add the sliced shiitake mushrooms and chopped bok choy, sautéing for 2-3 minutes until the vegetables are tender yet retain a slight crunch.
Return the beef to the skillet, sprinkle with sea salt, and toss everything together for 1 minute to meld the flavors.
Garnish the dish with sliced green onions and toasted sesame seeds before serving hot.