How to Make It
Place half of shrimp in a mini food processor; pulse 5 times or until chopped. Add onions, ginger, oil, and salt; pulse 2 to 3 times or until almost ground. Spoon into a medium bowl. Finely chop remaining shrimp. Stir chopped shrimp and peas into ground shrimp mixture.
Working with 1 gyoza skin at a time (cover remaining skins to prevent drying), place skin on a work surface, starchy side up. Moisten edge of skin with water. Spoon about 4 teaspoons shrimp mixture into center of each skin. Gather up and pleat edge of skin around filling, pressing to seal pleats; lightly squeeze skin to adhere to filling, leaving top of dumpling open. Place on a baking sheet lined with plastic wrap coated with cooking spray. Cover with a damp towel or paper towels to prevent drying. Repeat procedure with remaining gyoza skins and filling.
Line each tier of a 2-tiered bamboo steamer with cabbage or lettuce leaves. Arrange 9 dumplings, 1 inch apart, over leaves in each basket. Stack tiers; cover with steamer lid. Add water to a skillet to a depth of 1 inch; bring to a boil. Place steamer in pan; steam dumplings 8 minutes or until done, swapping tiers halfway through cooking. Discard leaves.