In a large skillet cook chicken in hot butter until lightly browned and no pink remains. Stir in chili powder, cumin, garlic, and cayenne; cook for 1 minute more. Cool slightly.
In a medium mixing bowl beat cream cheese, cheddar cheese, and sour cream until creamy and combined. Fold in chicken mixture, drained tomatoes and peppers, green onions, and cilantro. Cover and chill up to 24 hours. Spread mixture on 6 slices of bread. Top with avocado, cucumber, or tomato slices; add lettuce and remaining 6 slices of bread. (Or spread chicken mixture evenly over tortillas; top with lettuce, and avocado, cucumber, or tomato slices. Roll up tortillas. Makes 6 sandwiches.