Who did the argonauts play against during the game that had 19,423 fans in attendance?
CREATE TABLE "regular_season" (
  "week" real,
  "date" text,
  "opponent" text,
  "location" text,
  "final_score" text,
  "attendance" text,
  "record" text
);
SELECT "opponent" FROM "regular_season" WHERE "attendance"='19,423';