Prep the salmon. If using cooked fillets, remove the skin and any pin bones. Flake the salmon into bite-size pieces with a fork. If using canned salmon, drain well and lightly flake.
Salt the cucumber. Toss the sliced cucumber with a pinch of salt and let it sit for 5–10 minutes.
Pat dry with a paper towel to remove excess moisture. This keeps the salad from getting watery.
Make the dressing. In a large bowl, whisk together Greek yogurt, mayonnaise, Dijon, lemon juice, lemon zest, and olive oil. Season with a generous pinch of salt and pepper.
Add aromatics. Stir in dill, onion or shallot, and celery.
If using capers, add them now.
Fold in salmon and cucumber. Gently combine the flaked salmon and cucumber with the dressing until everything is evenly coated. Taste and adjust lemon, salt, and pepper as needed.
Chill briefly (optional but recommended). Cover and refrigerate for 15–30 minutes to let the flavors settle and the salad firm up.
Serve your way. Spoon onto lettuce cups, pile on toast, wrap in a tortilla, or serve with crackers and sliced avocado. Finish with a little extra dill or a squeeze of lemon.