Preheat the grill to medium-high heat.
In a small bowl, mix olive oil, garlic powder, paprika, salt, and pepper. Rub this mixture over the chicken breasts.
Grill the chicken for about 6-7 minutes on each side or until fully cooked and the internal temperature reaches 165°F. Remove from the grill and let it rest for 5 minutes before slicing.
In a large bowl, combine the mixed salad greens, diced mango, red bell pepper, red onion, avocado, and cilantro.
Squeeze lime juice over the salad and toss gently to combine.
Top the salad with sliced grilled chicken and sprinkle with feta cheese if desired. Serve immediately.