Marinate the chicken: In a bowl, whisk lemon juice, zest, olive oil, garlic, oregano, cumin, salt, and pepper.
Add the chicken and toss to coat. Cover and marinate for at least 20 minutes (up to 8 hours in the fridge).
Make the yogurt sauce: In a small bowl, combine yogurt, lemon juice, grated garlic, herbs, salt, and pepper. Stir until smooth.
Chill until serving.
Prep the veggies: Halve tomatoes, dice cucumber, slice red onion, and chop herbs. Slice olives and crumble feta, if using.
Cook the rice: Prepare brown rice according to package directions, or microwave cauliflower rice for a lighter base. Fluff with a fork and keep warm.
Sear the chicken: Heat a large nonstick skillet over medium-high.
Add the chicken in a single layer. Cook 3–4 minutes per side, until browned and cooked through. Rest 2 minutes, then slice if pieces are large.
Assemble the bowls: Divide rice among bowls.
Top with chicken, tomatoes, cucumber, onion, and olives. Add a spoonful of yogurt sauce and a sprinkle of feta and herbs. Finish with a squeeze of fresh lemon.
Taste and adjust: Add a pinch of salt, extra herbs, or another squeeze of lemon if needed.
Serve right away.