Slice the flank steak thinly against the grain into bite-sized strips and season with sea salt and black pepper.
In a small bowl, whisk together the coconut aminos, minced fresh ginger, and arrowroot powder until the mixture is smooth and no lumps remain.
Heat the toasted sesame oil in a large skillet or wok over medium-high heat until it begins to shimmer.
Add the beef strips to the pan in a single layer and sear for approximately 2 minutes until browned and caramelized, then remove the beef and set it aside.
Toss the broccoli florets and sliced red bell peppers into the same pan, stir-frying for 3-4 minutes until they are vibrant and tender-crisp.
Return the beef to the pan, add the minced garlic, and pour the coconut aminos sauce mixture over the ingredients.
Stir everything constantly for 1 minute as the sauce thickens into a glossy glaze that thoroughly coats the beef and vegetables.
Remove from heat and garnish with sliced green onions and toasted sesame seeds before serving immediately.