Cut beets, radishes, turnip, yellow carrot, purple carrot, and Jerusalem artichokes into very thin slices using a mandoline. Place slices in a bowl; add olive oil and red wine vinegar and stir gently with your fingers. Let marinate for 1 hour.
Heat bread cubes, pine nuts, and pumpkin seeds in a dry skillet over medium-low heat, stirring constantly, until toasted, about 5 minutes.
Arrange marinated slices on a serving plate. Top with toasted bread, pine nuts, and pumpkin seeds. Drizzle walnut oil on top; sprinkle with salt and pepper. Garnish with lettuce leaves.