On a rack in a broiler pan place mushroom caps, rounded side down. Drizzle with a small amount of olive oil. Sprinkle with salt and pepper. Broil 4-6 inches from the heat until mushrooms are tender (about 8 minutes). Reserve any juices. Cool mushrooms completely then chop them finely.

Combine mushrooms with shallots, garlic, chives, tarragon, vinegar, reserved mushroom juice, olive oil and salt and pepper. Cover and refrigerate until cold.

Serve over arugula or romaine lettuce leaves or over toasted French bread slices.