1. Peel shrimp, leaving tails intact. Butterfly shrimp by cutting each along its back, cutting to, but not through, inside curve of shrimp. Remove and discard vein. Place butterflied shrimp on a paper towel-lined plate; refrigerate until ready to use.
2. Place mushrooms, onions, and garlic in a mini food processor; pulse until minced. Place mushroom mixture in a medium bowl. Place pork in processor; pulse until ground. Add pork to mushroom mixture. Add tofu, oil, pepper, and salt to mushroom mixture; toss well to combine.
3. Working with 1 gyoza skin at a time (cover remaining skins to prevent drying), moisten outside edge of gyoza with water. Place 1 shrimp on skin, cut side down, so tail slightly points up; allow tail to hang over outside edge of skin. Spoon about 1 teaspoon filling over shrimp. Fold gyoza skin over shrimp so edges meet on top; press edges to seal. Moisten one side of seam with water; pleat seam 5 or 6 times. Place dumpling, seam side up, on a baking sheet lined with damp paper towels; cover with damp paper towels to prevent drying. Repeat procedure with remaining gyoza skins, shrimp, and filling.
4. Line 2 trays of a bamboo steamer with cabbage leaves; top with steamer lid. Add water to a large skillet to a depth of 1 inch; bring to a boil. Place steamer in pan; steam cabbage 4 minutes or until cabbage wilts. Arrange dumplings in trays on top of cabbage; steam 8 minutes or until done. Serve with Korean Dipping Sauce.