Ensure the salmon is very cold. Using a sharp knife, cut it into roughly 1/4-inch cubes and transfer them to a large bowl.
Finely chop the scallion, capers, and dill pickles, then add them to the salmon in the bowl.
Add the chopped fresh dill, juice of half a lemon, extra-virgin olive oil, and Dijon mustard. Gently stir to combine, being careful not to mash the salmon.
Taste and adjust with salt and freshly ground black pepper to your liking.
Cover the bowl with plastic wrap and chill in the refrigerator for 15–20 minutes to allow the flavors to meld.
When ready to serve, use a ring mold if you like, and serve the tartare with crostini, blinis, or avocado slices.