Place the flank steak in the freezer for 20 minutes to firm up, then slice against the grain into very thin strips.
In a medium bowl, whisk together the coconut aminos, toasted sesame oil, honey, grated Asian pear, minced garlic, grated ginger, and black pepper.
Add the sliced beef to the marinade, tossing to coat thoroughly, and let sit for at least 15 minutes.
Heat a large cast-iron skillet or wok over high heat until very hot.
Add the beef in a single layer, working in batches if necessary, and sear for 1-2 minutes per side until deeply browned and caramelized.
Remove the beef and quickly toss the baby spinach into the hot pan for 30 seconds until just wilted.
Serve the beef and spinach over the cooked jasmine rice, garnished with sliced green onions and sesame seeds.