Place trout into a deep large frypan, scatter with onion, vinegar, lemon, McCormick Dill and Fennel Seeds. Season to taste with McCormick Sea Salt and Black Pepper. Add enough cold water to cover the fish (it must be covered).
Cover with a lid or tin foil and bring to the boil (approx. 10 minutes to come to boil). Then once it is boiling, turn off the heat and allow the trout to stand in the water until cool.
To make the pickled cucumber and onion salad; combine all ingredients into a bowl and mix well.
Carefully remove the trout, place onto a board and scrape off the skin. Place the trout on a large serving dish with the refreshing pickled cucumber and onion salad.