Finely mince the carrot, red onion, cabbage, mushrooms, and bell pepper by hand or with a food processor, keeping the red onion separate for sautéing. A fine chop makes the filling easier to compress without creating a vegetable paste.

Warm the neutral oil in a large nonstick skillet over medium heat, then sauté the red onion and green onion for 1 to 2 minutes. The onion should soften and give off a fragrant aroma without browning deeply.

Stir in the remaining minced vegetables and sauté for 3 to 4 minutes, allowing released liquid to evaporate. The vegetables should soften, with no watery pool collecting beneath them.

Break the pressed tofu into small crumbles directly over the vegetables, then stir in the vegetarian oyster sauce, dark soy sauce, and black pepper. The seasoning should coat the tofu and vegetables evenly.

Continue cooking over medium heat for 4 to 5 minutes to reduce the remaining tofu moisture. The mixture should look loose and crumbly rather than wet.

Taste the filling, adjust the vegetarian oyster sauce if desired, and stir in the sesame oil. The finished mixture should taste savory and smell lightly nutty.

Move the filling to a bowl, mix in the cornstarch, and let it cool completely before wrapping. A spoonful pressed into a small mound should hold together instead of scattering.

Stir all the hoisin sauce ingredients together in a small bowl, adjusting the vinegar and sugar to taste. The dip should taste sweet, tangy, savory, and pleasantly spicy.

Fill a large bowl with room-temperature water and lightly oil a flat work surface and resting plate. The oil should form a thin film that keeps the hydrated wrappers from gripping the surfaces.

Briefly submerge one rice paper sheet, let excess water drain, and lay it flat on the prepared board. Allow a few seconds for it to become flexible enough to fold without cracking.

Place 1 heaping tbsp of filling just below the center, compact it, fold the bottom over it, bring both sides inward, and fold the packet toward the top to seal; repeat to make 15 dumplings. Each packet should feel snug, with overlapping edges, and rest separately on the oiled plate.

Heat a lightly oiled large nonstick skillet over medium heat and cook the dumplings thicker folded side down for 3 to 4 minutes, then flip and crisp the thinner side, working in 2 to 3 batches if needed. Small bubbles and a crisp underside signal when to turn, while the thinner side may finish sooner.

Transfer the cooked dumplings out of the skillet and serve promptly. The wrappers have their strongest crisp-and-chewy contrast immediately after frying.

Refrigerate leftover cooked dumplings in an airtight container. Keep them separate from the dipping sauce to protect the wrapper texture.

Reheat the dumplings in a lightly oiled skillet or air fryer until warm throughout and crisp again. The exterior should regain some crunch without becoming hard or scorched.