How to Make It
Preheat oven to 300°F. Spread walnuts in a single layer on a rimmed baking sheet, and toast in preheated oven until browned through center, about 20 minutes. Let cool.
Transfer walnuts to bowl of a food processor. Pulse until nuts reach a pebble-like consistency, about 8 times. Reserve 1/4 cup chopped walnuts.
Process remaining walnuts until they form a smooth nut butter, 1 to 2 minutes. With food processor running, add lemon juice, 1/2 cup water, vinegar, 11/2 teaspoons salt, and black pepper. Process until creamy and emulsified, about 1 minute. Transfer dressing to a bowl, and refrigerate until ready to use.
Place reserved 1/4 cup chopped walnuts in a small bowl; sprinkle with Urfa biber, and stir to combine. Set aside.
Using a mandoline, thinly shave radishes. Toss together radishes, parsley, tarragon, and mint in a medium bowl. Drizzle with olive oil; squeeze lemon wedge over mixture. Sprinkle with remaining 1/2 teaspoon salt.
To serve, gently toss together lettuce leaves and 3 tablespoons walnut dressing in a large bowl; divide among 6 plates. Top evenly with dressed radish-herb mixture and Urfa crumble. Serve with remaining walnut dressing.