In a bowl, whisk olive oil, lemon juice, garlic, oregano, salt, and pepper. Add chicken and marinate at least 20 minutes.
Heat a skillet over medium-high heat. Cook chicken strips 4–5 minutes per side until golden and fully cooked. Remove and let rest.
For the tzatziki, combine Greek yogurt, grated cucumber, garlic, olive oil, dill, lemon juice, salt, and pepper. Mix until creamy.
Assemble bowls: divide greens among 4 bowls, then top with cucumber, tomatoes, onion, olives, and feta.
Add grilled chicken on top and drizzle generously with tzatziki.
Serve immediately or store components separately for meal prep.