In a bowl, mix together olive oil, oregano, garlic powder, onion powder, smoked paprika, salt, and pepper to create the marinade. Add the chicken breasts to the bowl, ensuring they are well-coated. Cover and let marinate in the refrigerator for at least 30 minutes, ideally 1-2 hours.
Preheat a grill pan or skillet over medium-high heat. Once hot, add the marinated chicken breasts. Cook for about 6-7 minutes per side, or until the chicken is cooked through and no longer pink in the center. Remove from heat and let rest for a few minutes before slicing.
While the chicken is resting, assemble the bowls. Start with a base of cooked quinoa or rice in each bowl.
Top the grains with a generous portion of chopped romaine lettuce, diced tomatoes, diced cucumber, and sliced red onion.
Slice the rested chicken breasts into strips and arrange them on top of the vegetables in each bowl.
Sprinkle crumbled feta cheese over the bowls, and add a dollop of tzatziki sauce on top.
Finish with a sprinkle of fresh parsley for garnish.
Notes
Marinate the chicken for longer for enhanced flavor.