Roll each gyoza skin to 4 inches in diameter; set aside 8 wrappers.
Divide ricotta mixture into 8 portions (about 1 tablespoon each). Place 1 portion in the center of each of 8 skins. Make a well about 1 1/2 inches wide (about the diameter of a large egg yolk) in the center of each portion using the back of a tablespoon. Place 1 yolk (without breaking) in each well. Brush the edge of each gyoza skin with egg white. Cover each with 1 reserved gyoza skin, pressing edges firmly between your thumb and forefinger to seal ravioli tightly.
Bring a large pot of water to a gentle boil; carefully drop each ravioli into water. Cook 2 1/2 minutes or until dough is cooked and yolk is cooked but still runny. Remove each ravioli with a slotted spoon to a small plate. Sprinkle with chives and additional lemon rind, if desired. Serve immediately.