Use a mortar and pestle to break the peppercorns into smaller pieces. If you don't have a mortar and pestle, you can use coarsely cracked black pepper.
Slice the beef against the grain into ¼ inch thick slices. Lightly pound each slice with a meat tenderizer, then slice into bite-sized slices if needed.
Place the meat in a mixing bowl, then add 1 teaspoon of Shaoxing wine, ⅛ teaspoon of salt, ¼ teaspoon of cracked pepper, 1 teaspoon of cornstarch and 1 tablespoon of water. Mix well to combine. After that, drizzle ½ tablespoon of oil and toss to coat the beef. Set aside to marinate for about 15 minutes while you prepare other ingredients.
Cut the bell pepper into strips and then slice diagonally into diamond-shaped pieces (about ¾ - 1 cup sliced). Also slice onion into diamond-shaped pieces (about ½ cup sliced).
In a small bowl, add oyster sauce, soy sauce, dark soy sauce, sugar and the remaining Shaoxing wine, water and cornstarch. Stir well to combine.
Place a heavy-bottomed pan over medium heat and let it heat up until very hot. Increase the heat to medium-high and then add some oil to coat the pan. Add beef to the pan in a single layer and let it sear undisturbed for 20-30 seconds. Flip to cook the other side, or stir and cook for another 20-30 seconds until the beef is 80-90% cooked. Transfer to a plate.
Reduce heat to medium. Add a little more oil if needed, then add ginger and cook for 15-20 seconds until fragrant. Add garlic and sliced onions. Cook for about 10-15 seconds until fragrant, then add cracked peppercorns. Stir and cook for a minute. Add bell peppers and continue to stir and cook for about 30 seconds.
Increase the heat to medium-high. Give the sauce in Step 5 a quick stir, and then pour it into the pan. The sauce will start to bubble after a few seconds, then add the cooked beef back to the pan. Stir and toss quickly to coat everything with the sauce and just until beef is cooked through. Remove from the heat and serve hot right away.
To make it easier to slice the beef in Step 2, you can put it in the freezer for about a couple hours before slicing.