Slice the flank steak against the grain into thin strips and season with sea salt and black pepper.
Whisk together coconut aminos, toasted sesame oil, minced ginger, and minced garlic in a small bowl.
Heat 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 2-3 minutes, then remove from the pan.
Add the broccoli florets and sliced bell peppers to the same pan with a splash of water, covering for 2 minutes to steam-tenderize.
Return the beef to the pan and pour the sesame-ginger sauce over the mixture.
Toss everything together for 1-2 minutes until the sauce thickens slightly and coats the ingredients.
Garnish with sesame seeds before serving.