Thinly slice the steak against the grain and season to taste with salt and pepper.
Heat avocado oil in a large skillet over medium heat. Add steak and cook, stirring frequently, until fully cooked (about 5 minutes). Transfer steak to a plate and set aside.
Add soy sauce or tamari, beef stock, garlic, ginger and apple cider vinegar into the skillet and whisk until combined. Add broccoli and cook until sauce begins to reduce and the broccoli is tender, about 5 minutes.
Return steak to the skillet and toss to combine.
Serve with a drizzle of toasted sesame oil and sesame seeds, if desired.