Cook pasta according to package instructions. Rinse and drain the pasta with cold water. Set aside.
At the same time cook eggs for 10 minutes in boiling water. Transfer eggs into a bowl of cold water. Peel and coarsely dice the eggs.
Whisk mustard, relish, and mayonnaise in a large bowl until well combined. Add tuna, diced apple, red onion, eggs, parsley, and pasta. Stir to combine. If desired season to taste with salt and pepper.