To make the dough, mix the flour with warm water and knead for 10-15 minutes. There should be no need to add any flour on the board as you knead. Let the dough rest for 20 minutes while you make the filling.
To make the filling, partially thaw the spinach and lightly squeeze out most of the liquid. Mix with the rest of the ingredients.
To make the wrappers, divide the dough into 4 parts, roll each part out to about 12 inches in length, and divide each part into 12 balls. Roll each ball into a 3-inch disk. Place 1 Tbsp of filling in the center of each disk, then fold the dough over the filling to form a half-circle. Pinch together the top, then form 2 or 3 pleats down the sides and pinch together to seal. Note: a standard ravioli press will do a very nice job on these.
Heat 2 Tbsp of oil in a 12 inch heavy skillet over medium high heat. Lightly brown pot stickers until golden on the bottom, then pour 1 cup of water into the skillet and cover immediately. Cook over medium heat until most of the liquid is gone. Uncover and continue cooking until the liquid is entirely gone and the pot stickers are golden grown on the bottom.
Serve with a dipping sauce made from 2 Tbsp light soy sauce, 1 tsp sesame oil, and 1 Tbsp vinegar. You can also add chopped ginger and a small amount of chopped scallions to the dipping sauce, and a dash of chili oil if you like. (A very small amount of lemon juice can augment or replace the ginger.)
The filling will be distinctly green if prepared as above; most of the restaurants in my area seem to be trending toward less and less spinach in their pot stickers, apparently under the impression that more meat is classier. (Maybe it's cheap to way overdo the spinach, but you lose most of the unique character by making them just sausages in pasta...) Many grocery stores in the greater Boston area have frozen Peking Ravioli (pot stickers) apparently from the same company that supplies many of the area's restaurants.
Prepare the sauce well ahead of time if you add chopped ginger, to allow the ginger time to steep and properly flavor the sauce.
When I overcook them, I usually announce to my wife that I have prepared them "authentically", thus leading to our often using the word "authentic" to mean "screwed up". :-)
This recipe is from "Dim Sum", by Rhoda Lee, published by Taylor & Ng, San Francisco, 1977.