Marinate and Cook the Chicken In a small bowl, mix together the olive oil, oregano, lemon juice, salt, and pepper. Pour this marinade over the chicken breasts, coating them well. Allow the chicken to marinate for a minimum of 10 to 15 minutes. Meanwhile, preheat a grill pan or skillet over medium-high heat. Cook the chicken for approximately 6 to 8 minutes per side, or until it is thoroughly cooked and the juices run clear.
Prepare the Salad Base In a large mixing bowl, combine the cherry tomatoes, cucumber, red bell pepper, red onion, feta cheese, Kalamata olives, parsley, and basil (if using). Toss gently to mix.
Make the Dressing In a small bowl, whisk together the olive oil, red wine vinegar, Dijon mustard, minced garlic, salt, and pepper. Adjust seasoning to taste.
Assemble the Salad Slice the grilled chicken breasts into strips. Incorporate them into the salad bowl filled with the vegetables. Drizzle the dressing over the top, then gently toss the ingredients together until everything is evenly coated.
Serve Serve immediately, garnishing with additional fresh herbs if desired. This salad pairs beautifully with crusty bread or can be enjoyed as a light, standalone meal.