Place the flank steak in the freezer for 15 minutes to firm up, then slice against the grain into very thin strips.
In a medium bowl, whisk together the grated Korean pear, coconut aminos, toasted sesame oil, minced ginger, minced garlic, and black pepper.
Add the steak to the marinade, tossing to coat thoroughly, and let sit for at least 20 minutes to tenderize.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until shimmering.
Add the beef in a single layer, working in batches if necessary, and sear for 2-3 minutes until deeply caramelized and cooked through.
Remove the beef and quickly sauté the halved baby bok choy in the same pan for 2 minutes until the leaves are wilted but stems remain crisp.
Plate the cooked jasmine rice and top with the caramelized beef and sautéed bok choy.
Garnish with thinly sliced green onions and toasted sesame seeds before serving.