Grease an 8-inch spring-form pan and set aside. Stir together the hard-cooked eggs and mayonnaise. Evenly spread into the bottom of the spring-form pan and sprinkle the minced onion over the top. Stir together cream cheese and sour cream until smooth and spread over the onion layer. Cover and chill at least 3 hours in the refrigerator.
Once completely chilled, unwrap the pan and spread the lumpfish roe over the top. Run a knife around the edge of the pie and remove the side of the spring-form pan. Garnish with lemon wedges and parsley sprigs before serving.