Place chicken breasts in a zip top bag.
Prepare the marinade by blending together lime juice, cilantro, salt and pepper, garlic, cumin, chili powder, and olive oil. Pour half of the marinade in the bag with the chicken. Refrigerate for at least 30 minutes or up to 2 days.
Add sour cream to the other half of the marinade still in the blender. Blend until smooth. Refrigerate to use later.
Heat a skillet over medium high heat. Remove chicken from the marinade and cook 4-5 minutes on each side, or until done. Discard any remaining marinade. Let chicken rest for about 5 minutes before slicing.
While the chicken is cooking, roast the corn. Evenly spread the corn onto a baking sheet and season with salt and pepper. Roast under the broiler until lightly browned.
Prepare all salad ingredients. Chop the romaine lettuce, slice the tomatoes in half, slice the red onion, rinse the black beans, and slice the avocado.
Assemble the salad with a base of lettuce topped with chicken, tomatoes, roasted corn, black beans, cheese, avocado, and red onion. Drizzle the cilantro lime dressing.