Heat a grill or grill pan. Brush the chicken with the olive oil and sprinkle with 1/4 teaspoon salt and pepper to taste. Cook the chicken until done, about 3 to 4 minutes per side depending on thickness. The chicken should be white all the way through when pierced with a knife. Remove from the heat and let cool.
To make the dressing, combine the tomatillos, onion, jalapeño, and cilantro in the bowl of a food processor or blender and puree; add the avocado and blend until smooth. Season with lime juice, pepper to taste and the remaining ¾ teaspoon salt. Taste and add more salt if necessary. Reserve.
In a large bowl combine the lettuce, beans, tomato, cucumber, corn, tortilla chips and toss. Cut or tear the chicken into strips and add to the salad. Pour the dressing over the salad, toss well, and garnish with the cheese if using.