Season chicken breasts with salt, pepper, and a drizzle of olive oil. Grill over medium heat for 6–7 minutes per side or until fully cooked. Let rest, then slice thinly.
In a large bowl, combine chopped romaine lettuce, cherry tomatoes, cucumber, red onion, and celery. Toss lightly to mix.
In a separate small bowl, whisk together mayonnaise, Greek yogurt, Dijon mustard, lemon juice, honey, garlic powder, salt, and pepper until smooth.
Drizzle the dressing over the salad and toss gently to coat all ingredients evenly.
Top the salad with sliced grilled chicken. Serve immediately with extra dressing on the side.
Notes
For extra flavor, marinate the chicken in lemon and herbs for 30 minutes before grilling. You can also add avocado or nuts for texture.