In a large bowl, combine chicken, olive oil, oregano, salt, and black pepper. Coat the chicken well with the marinade.
Heat a skillet over medium heat. Add the chicken and cook for 5-7 minutes on each side until browned and cooked through. Remove from heat and let it rest.
In a large serving bowl, mix the romaine lettuce, cucumber, cherry tomatoes, olives, feta cheese, and diced avocado.
Slice the cooked chicken and add it to the salad. Drizzle with lemon juice, toss gently, and serve immediately.
Notes
Enjoy this salad as a light main meal or as a hearty side dish. Great with rustic bread or pita.