Marinate the chicken: In a bowl, combine olive oil, minced garlic, oregano, salt, pepper, and lemon juice. Add the chicken breasts and coat them thoroughly. Let them marinate for at least 15 minutes, or up to 4 hours in the refrigerator for maximum flavor.
Prepare the dressing: While the chicken marinates, whisk together all the dressing ingredients in a small bowl or jar. Set aside to let the flavors meld together.
Grill the chicken: Heat your grill or grill pan over medium-high heat. Cook the chicken for 6-7 minutes per side, or until the internal temperature reaches 165°F. The exact time depends on the thickness of your chicken breasts.
Rest the chicken: Remove the chicken from heat and let it rest for 5 minutes before slicing. This step is crucial – it keeps all those delicious juices inside the meat!
Assemble the salad: In a large bowl, combine the lettuce, tomatoes, cucumber, red onion, bell pepper, and olives. Toss gently with about half of the dressing.
Slice and serve: Slice the grilled chicken into strips. Divide the salad among plates, top with chicken slices, sprinkle with feta cheese, and drizzle with the remaining dressing.