Chicken with Roasted-Pepper Sauce

Heat broiler. Place peppers and garlic on a foil-lined baking sheet; broil 4 inches from heat source, skin side up, until peppers are blistered and blackened in spots and garlic is soft, about 20 minutes. Let cool, about 5 minutes. Use paper towels to rub off pepper skin; squeeze out garlic cloves (discard skins).

Make sauce: In a blender, combine peppers, garlic, vinegar, 2 tablespoons oil, and 3 to 4 tablespoons water; season generously with salt and pepper. Blend until emulsified.

Heat grill to medium; oil grates. Rub both sides of chicken breasts with remaining tablespoon oil; season generously with salt and pepper. Grill chicken, turning once, until browned and cooked through, 5 to 8 minutes per side. Serve with sauce, and garnish with arugula, if desired.