Cook the pasta in a pot of salted boiling water for 10-12 minutes (or as directed on the package). Drain the pasta, rinse it with water, and set it aside to cool down.
To make the dressing: In a medium bowl, mix the lemon juice, olive oil, yogurt, mustard, garlic powder, salt, black pepper, and chopped parsley.
In a large serving bowl, combine the cooled pasta, tuna, cucumber, onion, tomatoes, olives, and capers. Pour the dressing over the top and gently toss everything together until it's mixed well.
Serve your diet tuna pasta salad immediately. Enjoy