1. Prepare the Mung Bean Sprouts:
* Rinse the mung bean sprouts thoroughly under cold running water in a colander.
* Pick out any discolored sprouts or loose green husks (the tiny seed shells).
* Drain them very well. You can even give them a gentle spin in a salad spinner or pat them dry with paper towels. Excess water will make the stir-fry soggy and prevent crisping. Set aside.

2. Prepare Aromatics and Other Vegetables (if using):
* Mince the garlic and ginger.
* Cut the scallions into 1-inch pieces, keeping the white/light green parts separate from the dark green tops.
* If using carrots or bell peppers, julienne or thinly slice them.
* If using tofu, ensure it’s pressed and cubed. If using cooked shrimp or chicken, have it ready.

3. Mix the Sauce:
* In a small bowl, whisk together the soy sauce, sesame oil, sugar, white pepper, and chicken broth/water (if using).
* If you want a slightly thicker sauce, prepare the cornstarch slurry by mixing ½ teaspoon of cornstarch with 1 tablespoon of cold water in a separate tiny bowl until smooth. Set both the sauce and slurry aside.

4. Heat the Wok/Skillet:
* Place a wok or large, heavy-bottomed skillet over high heat. Allow it to get very hot – you should see a slight shimmer or wisps of smoke.

5. Stir-Fry the Aromatics (and optional protein/harder vegetables):
* Add 1-2 tablespoons of vegetable oil to the hot wok. Swirl to coat the bottom.
* Add the minced garlic and ginger. Stir-fry for about 15-30 seconds until fragrant. Be careful not to burn them.
* If using firm tofu, add it now and stir-fry until lightly golden.
* If using carrots or bell peppers, add them now and stir-fry for 1-2 minutes until they are slightly tender-crisp.
* Add the white/light green parts of the scallions and stir-fry for another 30 seconds.

6. Add the Mung Bean Sprouts:
* Add the thoroughly drained mung bean sprouts to the wok.
* Stir-fry quickly and continuously over high heat for 1-2 minutes. The goal is to heat them through and cook them lightly so they retain their crispness. They will wilt slightly. Avoid overcooking, as they can become watery and limp.

7. Add the Sauce:
* Pour the prepared sauce mixture over the sprouts. Toss everything together quickly to coat evenly.
* If using the cornstarch slurry, give it a quick stir (as cornstarch settles) and pour it into the wok. Stir continuously until the sauce thickens slightly and turns glossy, about 30 seconds.

8. Finish and Serve:
* Stir in the green parts of the scallions.
* If using cooked shrimp or chicken, add it now and toss just to heat through.
* If you like a bit of heat, add a pinch of chili flakes.
* Turn off the heat.
* Immediately transfer the stir-fried mung bean sprouts to a serving dish.
* Garnish with toasted sesame seeds, if desired. Serve hot.