Step 1: Marinate the Chicken

1. In a bowl, whisk together olive oil, lemon juice, minced garlic, oregano, salt, and pepper.
2. Add the chicken and coat evenly. Cover and let marinate in the refrigerator for at least 30 minutes (or up to 8 hours for deeper flavor).

Step 2: Make the Tzatziki Sauce

1. Grate the cucumber and squeeze out excess water using a paper towel or cheesecloth.
2. In a bowl, mix Greek yogurt, cucumber, lemon juice, garlic, fresh dill (or mint), salt, and pepper.
3. Cover and refrigerate for at least 30 minutes to let the flavors meld.

Step 3: Cook the Chicken

1. Heat a grill pan, skillet, or outdoor grill over medium-high heat.
2. Cook the chicken for 5-7 minutes per side until golden brown and fully cooked (internal temperature of 165°F/75°C).
3. Let rest for 5 minutes, then slice into strips.

Step 4: Assemble the Bowls

1. Divide the cooked rice (or quinoa) into serving bowls.
2. Arrange the grilled chicken, cherry tomatoes, cucumber, red onion, feta cheese, and olives on top.
3. Drizzle with tzatziki sauce and serve with warm pita bread or naan if desired.