Preheat your grill or stovetop grill pan over medium-high heat.
In a small bowl, mix together the olive oil, garlic powder, smoked paprika, oregano, salt, and pepper. Rub this mixture all over the chicken breasts.
Grill the chicken for about 6-7 minutes per 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.
While the chicken is resting, prepare the feta sauce by combining the Greek yogurt, lemon juice, and fresh dill in a small bowl. Mix until smooth and set aside.
In a large bowl, combine the cooked quinoa, cherry tomatoes, cucumber, baby spinach, red onion, feta cheese, and Kalamata olives. Toss gently to combine.
To serve, divide the quinoa salad among bowls, top with sliced grilled chicken, and drizzle with the feta sauce.