Drain the cottage cheese in a fine mesh strainer for 15 minutes. This removes excess whey and keeps the topping thick enough to hold its shape.
Blend the drained cottage cheese, cream cheese, chopped dill, lemon juice, lemon zest, Dijon mustard, and black pepper in a food processor until completely smooth.
Transfer the whipped cottage cheese to a covered container and refrigerate it for 20 minutes. Chilling gives the mixture a firmer, creamier texture.
Cut the cucumbers into 1/2-inch rounds and pat the surfaces dry. Arrange the rounds in a single layer on a serving platter.
Spoon or pipe a generous mound of whipped cottage cheese onto each cucumber round. Fold a small piece of smoked salmon over the top.
Garnish the bites with capers, red onion, fresh dill, and lemon zest. Serve immediately, or refrigerate for no more than 1 hour before serving.