This is an excellent stir-fry, but does take a little prep.
Freeze 10-12 oz of sirloin for 45 minutes or so, to make it easier to slice. Cut it into ~1⁄8 inch strips.
Mix the white of one egg, 1 tbsp of corn starch, 1 tsp of baking soda and a pinch of salt. Toss the beef in it, making sure each piece is coated.
Let chemistry happen with the beef for 15-20 minutes. Meanwhile, prep some vegetables. A clove or two of garlic and about the same amount of ginger, cut fine. Half a yellow onion, cut into thin half-rounds. Several scallions - I used 2, but 4 or 5 might be better, cut into 2 inch lengths. Some red bell pepper, cut into strips the same size as everything else. And for some heat, half a dozen dried arbol chillis left mostly whole but with most of the seeds removed. And some broccoli florets, cut fairly small, about two or three cups.
For a sauce, mix 3 tbsp oyster sauce, a tbsp of mirin, a tbsp of rice wine vinegar and a tbsp of sesame oil.
In a wok with a cup and a half of oil deep fry the beef, probably in two batches of two or three minutes each. Use tongs or chopsticks to make sure the beef is separated. Remove to a plate.
Drain off and discard most of the oil. Add the ginger and garlic, stir for a few seconds. Add the chillis, shallots and onion. Let fry for a minute or two. Add the broccoli and stir-fry for a couple of minutes. Add the pepper and fry for another couple of minutes. Add the beef and stir in the sauce then let everything get comfortable for a couple of minutes.
Serve over rice.