Step one: Make the filling
In a small bowl, soak the peppercorns in 1/3 cup of lukewarm water for at least 1 hour, then strain out peppercorns and discard. Wrap the zucchini in a clean cheesecloth or tea towel and squeeze to remove excess water. In a medium bowl, add the lamb and slowly pour in the peppercorn-infused water, a few drops at a time, and use your hands to mix it in well until the water is fully absorbed. Add the scallions, wine, ginger, soy sauce, and salt, and mix well until fully incorporated. Gently fold in the zucchini and mix until well combined.
Step two: Make the dumplings
Cup your non-dominant hand like you’re holding a light bulb and press a dumpling wrapper into your palm so the center forms a pocket and the edges lie flat. With your dominant hand, use a fork to add about 1 tablespoon of the filling to the center of the wrapper, then lightly pat the filling down with the fork to get rid of any air bubbles (this will also make the dumpling easier to seal).
Fold the dumpling into a half-moon, pinching it shut with your thumbs and forefingers, then press the center of the dumpling while pulling on the corners to push out any air bubbles and shape it into a curved crescent. Inspect the dumpling for any holes where the filling could leak out and pinch them shut. Repeat steps 2 and 3 for the rest of the wrappers to make 24 dumplings.
Step four: Cook the dumplings
In a small bowl, whisk together the flour, vinegar, and 1 cup of water until combined to make a slurry. Brush the oil in a medium cast iron or non-stick skillet and heat over medium-high heat, until the oil starts to shimmer. Add 6 dumplings with the folded edges lying flat on the pan, spacing them 1 inch apart, then slowly pour in just enough of the slurry to come one-third of the way up the dumplings. Partially cover the pan, leaving a small gap for steam to escape. Increase heat to high and cook for 2 minutes for cast iron (1 minute for non-stick). Lower heat to medium for 2 minutes for cast iron (3 minutes for non-stick). Then lower heat to low for 2 to 3 minutes for cast iron (3 minutes for non-stick).
Cook until the water has evaporated, leaving a paper-thin disc of golden-brown starch on the bottom of the pan. Remove from heat and slide a thin, flexible spatula around the rim of the pan to loosen the edges of the starch disc, then carefully slide the spatula underneath and flip the dumplings onto a plate in one piece, crispy-side-up. Clean skillet and repeat steps 4 and 5 for remaining dumplings. Serve immediately.