Slice the sirloin steak against the grain into thin, bite-sized strips and season with sea salt and black pepper.
Whisk together the tamari, arrowroot powder, and minced ginger in a small bowl to create the stir-fry sauce.
Heat the toasted sesame oil in a large wok or skillet over medium-high heat until shimmering.
Add the steak strips to the pan in a single layer, searing for 2 minutes until browned, then remove and set aside.
In the same pan, add the broccoli florets and a splash of water, covering for 2 minutes to steam until bright green and tender-crisp.
Stir in the minced garlic and cook for 30 seconds until fragrant, being careful not to burn it.
Return the steak to the pan and pour the tamari sauce over the mixture, tossing constantly for 1 minute until the sauce thickens and coats everything.
Serve the stir-fry over the cooked white rice and garnish with sliced green onions.