Heat grill to medium-high. Season chicken with coriander, oregano, salt, pepper, and 2 tablespoons olive oil. Grill, covered, turning halfway through, until slightly charred and the thickest part of the breast registers 165ºF when probed with a thermometer, 18 to 22 minutes. Let rest for another 5 minutes, then slice.
Meanwhile, make dressing. Whisk olive oil, red wine vinegar, and parsley in a small bowl and season with salt and pepper.
Divide lettuce, cucumbers, tomatoes, avocado, feta, and olives among four serving bowls. Top with sliced chicken, then drizzle with dressing.
