Preheat your grill or grill pan over medium-high heat.
In a small bowl, whisk together olive oil, balsamic vinegar, garlic powder, dried oregano, salt, and pepper.
Coat the chicken breasts in half of the dressing, reserving the other half for later.
Grill the chicken for 6-7 minutes on each side or until fully cooked and the internal temperature reaches 165°F (75°C). Remove from the grill and let it rest for 5 minutes.
While the chicken is resting, prepare the salad in a large bowl by combining the salad greens, cherry tomatoes, cucumber, bell pepper, red onion, and feta cheese.
Slice the grilled chicken into strips.
Top the salad with the sliced chicken and drizzle the reserved dressing over everything.
Toss gently to combine, ensuring an even distribution of dressing. Serve immediately.