Cipollini onions are about the size of golf balls and usually have a flattened shape. They’re sweeter than yellow onions and great for caramelizing. If you can’t find cipollini, Vidalia or Walla Walla onions are good substitutes.
Fish should easily come free of pan when turning. If it does not, let it cook a bit longer. Fish should flake with a fork when done, and minimum internal temperature should be 145°.