1. Wash chicken and pat dry. Place it in a pot of cold water (use enough to cover). Bring to a boil, Reduce heat to a gentle boil and cook for 40 minutes. (Optionally, cook in a grill pan over medium-high heat, 5 minutes per side). Let cool. Tear the chicken into strips or cut.
2. In a medium skillet heat 1 1/2 tablespoons oil over medium-high heat. Add the mushrooms and cook over a medium heat for 3-5 minutes. Let cool.
3. Tear lettuce into bite size pieces.
4. In a separate bowl, combine mayonnaise, sour cream, garlic powder, onion powder, Italian seasoning, salt and pepper. Mix well, adding a little milk or cream as desired. Taste and adjust seasonings to taste.
5. Arrange lettuce on 4 plates. Place chicken and mushrooms over the lettuce. Add tomatoes and top with grated cheese.
6. Pour the dressing over each portion and serve.