Whisk together the marinade ingredients. Add the beef, toss to coat, and refrigerate for 1 hour. This can be done in a bowl or a zip-top bag.
Mix together the sauce ingredients. If desired, this can be done earlier in the day and refrigerated.
Heat 1 tablespoon oil in a 12-inch nonstick skillet or wok set over medium-high heat. Stir-fry the beef until it reaches a point just a shade below your preferred degree of doneness. (I like to see a little pink in the center at this point.) Remove to a plate.
Add the remaining tablespoon of oil followed by the garlic, ginger, and pinch of salt and sugar; stir-fry 30 seconds.
Add the onion and cook until beginning to soften, about 2 minutes. Stir in the broccoli and cook until crisp-tender, about 4 to 5 minutes.
Return the beef to the pan, add the sauce*, and cook, stirring to make sure everything is evenly coated, until the sauce is thickened, about 2 to 3 minutes.
Serve over rice or toss with noodles, and sprinkle with desired garnishes.