To pickle the red onion, combine all the ingredients in a mason jar and stir to dissolve the sugar and salt. Allow to sit and pickle for about an hour before eating. Then keep the leftovers in the refrigerator to enjoy on salads, sandwiches, tacos, nachos, etc.
This is pretty much an assembly-only recipe! To assemble, spread the toasted English muffins with cream cheese. Top with a layer of cucumber and tomato, then follow with the smoked salmon. Top with pickled red onion and if desired, capers and fresh dill. Freshly ground black pepper is a lovely finish.