Process the farmer's cheese, finely chopped walnuts, and yogurt in a food processor until smooth.
Transfer the cheese to a bowl and mix with herbs, garlic, and salt. Shape into a ball, cover, and refrigerate for 4 hours.
Line a small serving platter with several lettuce leaves and carefully transfer the cheese ball to the platter. Press the coarsely chopped walnuts into the ball so they more or less cover it. Serve with the toasted pita triangles.