Make chipotle ranch dressing. In a blender combine all ingredients for dressing including yogurt, buttermilk, dill, parsley, chipotle, garlic, onion powder, and lime juice. Puree until smooth. Season dressing with salt and pepper. Reserve half of the dressing and set aside.
Pour remaining dressing over chicken, tossing to coat. Let sit for 30 minutes.
Meanwhile, prepare remaining salad ingredients. Fill a medium bowl with ice water and set aside.
Bring a medium pot of water to a boil over high heat. Add green beans and cook for 2 minutes. Add corn and cook for 1 more minute. Remove from heat and immediately shock green beans and corn in ice water. Drain and set aside.
Heat grill to medium heat. Remove chicken from marinade and cook until juices run clear, about 5 minutes. Season chicken with salt and pepper and let sit for 10 minutes. Cut chicken into bite-size chunks.
Portion chopped romaine into 4 bowls. Top with green beans, corn, avocado, sliced shallots, pepperoncini, and chicken. Sprinkle cotija on top and serve with reserved chipotle ranch dressing.