01 - Combine mayonnaise, sour cream, lemon juice, vinegar, parsley, chives, tarragon, basil, anchovy fillets if using, garlic, salt, and pepper in a blender or food processor. Blend until completely smooth and creamy. Taste and adjust seasoning as desired. Transfer to an airtight container and refrigerate until ready to serve.
02 - Place mixed salad greens, cucumber, radishes, and snap peas in a large serving bowl. Drizzle with approximately 1/2 cup of the prepared Green Goddess dressing and toss gently to evenly coat all vegetables. Arrange avocado slices on top and sprinkle with fresh herb garnish. Serve immediately with remaining dressing on the side.