If cooking chicken for this recipe: trim visible fat from 4 chicken breasts and cut each lengthwise into thirds.
In a medium saucepan combine 1 can chicken stock, 2 cans water, and 1–2 teaspoons Italian herb blend or poultry seasoning and bring to a boil; add chicken breasts, reduce heat to low, and simmer 15 minutes or until cooked through.
Drain the cooked chicken in a colander and let cool until easy to handle, then dice into about 3/4-inch pieces.
While the chicken cools, slice the basil leaves, wash if needed, and slice the green onions; measure and coarsely grate the Parmesan.
Whisk the mayonnaise and buttermilk together in a bowl until smooth, then stir in the sliced green onion, grated Parmesan, and basil.
Add the dressing to the diced chicken and gently toss until evenly coated; season with salt and freshly ground black pepper to taste.
Serve immediately or chill briefly before serving.