Marinate the chicken: In a bowl, mix olive oil, lemon zest and juice, garlic, oregano, cumin, smoked paprika, salt, and pepper. Add chicken and toss to coat.
Cover and refrigerate for at least 30 minutes, or up to 8 hours.
Cook the grains: Prepare quinoa, rice, or farro according to package directions. Fluff with a fork and set aside. For extra flavor, cook in low-sodium chicken broth.
Make the tzatziki: Grate the cucumber, then squeeze out excess water using a clean towel or paper towels.
Stir together Greek yogurt, cucumber, lemon juice, olive oil, garlic, dill, and salt. Taste and adjust salt or lemon as needed. Chill until serving.
Prep the veggies: Halve tomatoes, dice cucumber, slice red onion, and chop greens.
Pit and halve olives. Keep everything in separate containers if prepping ahead.
Cook the chicken: Heat a large skillet or grill pan over medium-high. Lightly oil the surface.
Cook chicken 4–6 minutes per side, depending on thickness, until the center reaches 165°F (74°C). Rest 5 minutes, then slice.
Assemble the bowls: Spoon grains into bowls. Add greens, tomatoes, cucumbers, onion, and olives.
Top with sliced chicken and a generous dollop of tzatziki. Sprinkle with feta and herbs. Finish with a squeeze of lemon and a drizzle of olive oil if you like.
Serve: Enjoy warm or at room temperature.
Add extra tzatziki on the side for dipping.