Wash, core and dice the pear. Cut the smoked salmon into strips. Chop the onion as finely as possible. Put everything in a bowl.
In a separate small bowl, mix the oil, vinegar, salt, pepper and water with the mustard and horseradish with a small whisk. Squeeze the garlic clove through a garlic press, add and mix.
Pour the marinade over the pear, salmon and onion mixture and stir everything through. Let it steep in the refrigerator for 30 minutes.