In a medium bowl, combine the diced salmon, avocado, red onion, and capers.
In a separate small bowl, whisk together the Dijon mustard, soy sauce, lemon juice, olive oil, salt, and pepper.
Pour the dressing over the salmon mixture and gently fold to combine, being careful not to mash the avocado.
Taste and adjust seasoning if necessary.
Cover the bowl with plastic wrap and refrigerate for about 15-30 minutes to allow the flavors to meld.
Serve chilled, garnished with chopped chives, alongside tortilla chips or cucumber slices.