Cook the rotini pasta according to package instructions. Drain and rinse under cold water to cool.
Preheat the grill to medium-high heat. In a bowl, toss the chicken breasts with olive oil, garlic powder, Italian seasoning, salt, and pepper.
Grill the chicken for about 6-7 minutes on each side or until fully cooked and juices run clear. Remove from grill and let rest for 5 minutes before slicing.
In a large bowl, combine the cooked pasta, cherry tomatoes, cucumber, red onion, and feta cheese.
In a small bowl, whisk together the balsamic vinegar, olive oil, Dijon mustard, honey, salt, and pepper until well combined.
Pour the vinaigrette over the pasta salad and toss to coat evenly.
Add the sliced grilled chicken on top and garnish with fresh basil. Serve immediately or chill in the refrigerator for 30 minutes for enhanced flavor.