Bring a large pot of salted water to a boil. Add the whole wheat penne pasta and cook according to package instructions until al dente, about 10-12 minutes.
While the pasta cooks, preheat a grill pan or skillet over medium-high heat.
In a small bowl, mix garlic powder, paprika, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Rub this spice mixture evenly over both sides of the chicken breasts.
Add olive oil to the hot grill pan and cook the chicken breasts for 6-7 minutes per side, or until fully cooked and internal temperature reaches 165°F (74°C). Remove from heat and let rest for 5 minutes.
Drain the cooked pasta and rinse under cold water to cool it down. Set aside.
Slice the grilled chicken breasts into bite-sized pieces.
In a large mixing bowl, combine the cooled pasta, sliced chicken, cherry tomatoes, diced cucumber, diced red bell pepper, and chopped red onion.
In a separate small bowl, whisk together the Greek yogurt, lemon juice, Dijon mustard, chopped parsley, 1/4 teaspoon salt, and 1/8 teaspoon black pepper until smooth.
Pour the dressing over the pasta and chicken mixture. Toss gently until everything is evenly coated.
Refrigerate the salad for at least 15 minutes before serving to allow flavors to meld. Serve chilled or at room temperature.