Set oven rack about 6 inches from the heat source and preheat the oven's broiler.
Coat poblano peppers with vegetable oil and place on a baking sheet.
Cook peppers under the broiler until blistered and scorched, about 10 minutes. Transfer peppers to a bowl and cover with plastic wrap until peppers are cool enough to handle. Remove skin from peppers.
Blend peppers, mayonnaise, lime juice, and garlic in a blender until dressing is smooth. Add cilantro, salt, and pepper to dressing and process until cilantro is incorporated but not smooth.
