Make the chicken marinade: In a bowl, mix 3/4 cup Greek yogurt, 2 tablespoons olive oil, zest and juice of 1 lemon, 1 tablespoon red wine vinegar, 3 minced garlic cloves, 2 teaspoons dried oregano, 1 teaspoon ground cumin, 1 teaspoon smoked paprika, 1/2 teaspoon ground coriander, 1 teaspoon salt, and 1/2 teaspoon black pepper.
Marinate the chicken: Add chicken thighs to the marinade and toss to coat.
Cover and chill for at least 30 minutes, or up to 8 hours for deeper flavor.
Cook the grains: Prepare brown rice, quinoa, or farro per package directions. Fluff and set aside. For extra flavor, stir in a squeeze of lemon and a drizzle of olive oil.
Prep the veggies: Halve the cherry tomatoes, dice the cucumber, thinly slice the red onion, and chop the romaine or spinach.
Pit and slice olives. Crumble feta. Chop dill or parsley.
Make the tzatziki: Squeeze excess water from 1 grated cucumber.
Mix with 1 cup Greek yogurt, 1 tablespoon lemon juice, 1 small minced garlic clove, 1–2 tablespoons chopped dill, 1 teaspoon olive oil, and a pinch of salt and pepper. Chill to thicken.
Cook the chicken: Heat a large skillet or grill pan over medium-high. Lightly oil the surface.
Shake excess marinade off the chicken and cook 5–6 minutes per side, until nicely browned and the internal temp reaches 165°F (74°C). Rest 5 minutes, then slice.
Assemble the bowls: Divide grains among bowls. Top with greens, sliced chicken, tomatoes, cucumber, red onion, olives, and feta.
Spoon over tzatziki. Finish with fresh herbs and a squeeze of lemon.
Optional warm pita: Warm whole-wheat pitas in a dry skillet for 30 seconds per side. Serve on the side or cut into wedges for dipping.