Drain the liquid from the canned tuna thoroughly using a fine-mesh strainer or the can lid.
In a medium mixing bowl, combine the cottage cheese and lemon juice. Mash slightly with a fork if a smoother consistency is desired.
Add the drained tuna to the bowl and use a fork to flake the fish into small pieces.
Incorporate the Dijon mustard, minced red onion, diced celery, and chopped dill into the mixture.
Season with ground black pepper and stir until the ingredients are uniformly distributed.
Serve immediately or refrigerate for 30 minutes to allow flavors to meld.