Slice the flank steak against the grain into thin strips and season with the sea salt and black pepper.
In a small bowl, whisk together the tamari, honey, toasted sesame oil, minced ginger, and minced garlic to create the stir-fry sauce.
Heat the avocado oil in a large skillet or wok over medium-high heat until shimmering.
Add the beef strips in a single layer and sear until browned, about 2 minutes per side, then remove from the pan and set aside.
Add the broccoli florets to the same pan with a splash of water, cover immediately, and steam for 3 minutes until tender-crisp.
Return the beef to the pan, pour in the prepared sauce, and toss everything together for 1 minute until the glaze thickens and coats the ingredients.
Serve the stir-fry over the warm cooked brown rice and garnish with sesame seeds and red pepper flakes.