Rub the chicken breast with the olive oil, lemon juice, garlic, salt, pepper, and oregano. Let it marinate for at least 15 to 20 minutes.
Cook the chicken in a hot grill pan or on an outdoor grill for 5 to 6 minutes per side, until golden brown and fully cooked through.
Let it rest for a few minutes, then slice it into strips.
In a large bowl, mix together the salad leaves, tomatoes, cucumber, and red onion.
Cut the avocado into cubes and add it to the salad.
Mix together the dressing ingredients, then drizzle it over the salad.
Place the grilled chicken strips on top and serve immediately.