Put avocado, lemon juice, parsley, basil, scallions, garlic and anchovies (if using) in food processor. Process until smooth. Add mayonnaise and Greek yogurt and pulse until blended. Season to taste with salt and pepper.
Transfer to serving bowl, cover and chill. Serve with assorted vegetables.
Adapted from Cooking Light. For a vegan version, leave out the anchovies and add a few dashes of soy sauce if you like.