Cook the base: Prepare brown rice or quinoa according to package directions. Fluff and let cool. For a lighter option, sauté riced cauliflower in a nonstick pan with a pinch of salt for 5–7 minutes until tender.
Make the chicken marinade: In a bowl, combine lemon zest and juice, olive oil, minced garlic, oregano, cumin, salt, and pepper.
Whisk until emulsified.
Prep the chicken: Pat chicken dry. Slice breasts horizontally into thinner cutlets for faster, even cooking. Add to the marinade, toss to coat, and let sit 20–30 minutes at room temperature (or up to 8 hours in the fridge).
Mix the sauce: Combine Greek yogurt, grated and squeezed-dry cucumber, lemon juice, dill, garlic, salt, and pepper.
Stir until smooth. Adjust lemon and salt to taste. Cover and chill.
Chop the veggies: Halve the cherry tomatoes, dice the cucumber, thinly slice the red onion, and chop the bell pepper.
Roughly chop olives and herbs. Toss tomatoes, cucumber, onion, and bell pepper with a pinch of salt and a splash of red wine vinegar if using. Set aside.
Cook the chicken: Heat a large skillet or grill pan over medium-high.
Lightly oil the surface. Cook chicken 3–5 minutes per side, until browned and the internal temperature reaches 165°F (74°C). Rest 5 minutes, then slice.
Assemble the bowls: Divide rice or quinoa among containers.
Top with sliced chicken, the chopped veggie mix, olives, and herbs. Add a sprinkle of feta if using.
Portion the sauce: Spoon sauce into small lidded condiment cups, or keep it separate to add just before eating. Add lemon wedges if you like extra brightness.
Final taste check: If meals will be eaten cold, season the chicken and grains just a touch more than usual—chilled foods can taste less seasoned.