In a small bowl, whisk together olive oil, lemon juice, oregano, garlic powder, salt, and pepper. Place chicken breasts in a resealable bag or shallow dish and pour marinade over the chicken, ensuring it's well coated. Let it marinate in the fridge for at least 30 minutes (or up to 4 hours for more flavor).
While the chicken is marinating, prepare the quinoa. In a medium saucepan, combine rinsed quinoa and vegetable broth (or water). Bring to a boil, then reduce to a simmer, cover, and cook for 15 minutes or until the quinoa is fluffy and liquid is absorbed. Remove from heat and let it sit covered for 5 minutes, then fluff with a fork.
Preheat a grill or grill pan over medium-high heat. Remove chicken from the marinade and discard the marinade. Grill the chicken for about 6-7 minutes per side, or until fully cooked and internal temperature reaches 165°F (75°C). Remove from grill and let it rest for 5 minutes before slicing.
In each meal-prep container, add a base of quinoa. Top with sliced grilled chicken, cherry tomatoes, cucumber, bell pepper, red onion, and kalamata olives evenly across the containers. Sprinkle feta cheese over the top.
For garnish, sprinkle fresh parsley over the assembled bowls. Seal the meal prep containers and store in the refrigerator for up to 5 days.
Notes
Add a lemon wedge to each meal prep bowl for a pop of color and freshness.