Season chicken breasts with salt and pepper, then grill or pan-sear over medium-high heat for 6 to 7 minutes per side until the internal temperature reaches 165°F (74°C).
Transfer chicken to a cutting board and allow to rest for 5 minutes before dicing into 1/2-inch cubes.
In a high-speed blender or food processor, combine the avocado, Greek yogurt, lime juice, garlic, olive oil, and cilantro.
Pulse the dressing ingredients until the mixture is smooth and creamy; thin with a teaspoon of water if necessary to reach desired consistency.
In a large mixing bowl, combine the chopped romaine, cherry tomatoes, diced cucumber, red onion, black beans, and corn.
Add the diced chicken to the vegetable mixture.
Drizzle the avocado dressing over the salad and toss thoroughly with large spoons until all components are evenly coated.
Divide into four chilled bowls and serve immediately.