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
Recipe courtesy of Food Network Magazine