Marinated Greek Chicken Skewers | 1 1/2 lbs. boneless, skinless chicken breast, cut into 1-inch pieces 4 Tbsp. extra virgin olive oil, divided 4 garlic cloves, crushed 1-2 tsp. dried oregano 1 tsp. salt 1 tsp. ground black pepper 2 Tbsp. freshly squeezed lemon juice 1/2 red onion, quartered 1 green bell pepper, cut into 1 inch pieces 1 red bell pepper, cut into 1 inch pieces