In a small bowl, mix together the greek yogurt, lemon juice, oregano, garlic powder, salt, and pepper. Add the chicken chunks to a ziplock bag and pour the yogurt mixture over the top. Seal the bag and toss to coat. Refrigerate for thirty minutes.
Thread the marinated chicken chunks onto skewers, alternating with chunks of red pepper and red onion.
Grill on medium high heat for 6 to 8 minutes per side, until juices run clear. Alternatively, line a baking sheet with foil and place a cooling rack on top. Place the skewers on the cooling rack, and bake at 425 for 25-30 minutes.