Make the dressing: Whisk the mayonnaise, buttermilk, vinegar, onion powder, chives, parsley, garlic, 1/2 teaspoon salt and a few grinds of pepper in a small bowl; set aside.
Make the salad: Put the red onion in a bowl and cover with cold water; let soak 10 minutes, then drain.
Combine the lettuce in a large bowl and add the radishes, carrots, cucumbers, bell pepper and red onion. Toss with the dressing and season with salt.
Photograph by Con Poulos
Courtesy of Food Network Magazine