Pulse capers, until coarsely chopped, in a food processor fitted with a steel blade. Add salmon, dill, oil and lemon zest; pulse until salmon is finely chopped and well-mixed. Stir in red onion. Serve with kettle-style potato chips, sesame crackers or toasts. If you assemble the hors d'oeuvres (rather than letting guests make their own), top each tartare-covered toast or chip with a thin slice of lemon, rind and all.