Kohlrabi Caesar Salad

• 4 ounces smoked trout, broken into bite-size pieces
• 1 teaspoon finely grated lemon zest
• ¼ teaspoon crushed red pepper flakes
• ½ cup finely chopped mixed tender herbs (such as parsley, chives, and/or fennel fronds), divided
• ¼ cup plus 2 tablespoons olive oil; plus more for drizzling

Kosher salt, freshly ground pepper

• 4 slices ¼-inch-thick country-style bread
• 1 large egg yolk
• 1 garlic clove, finely grated
• 1 teaspoon plus 1 tablespoon fresh lemon juice
• ⅓ cup vegetable oil
• 2 pounds kohlrabies (about 5 medium), peeled, halved lengthwise, very thinly sliced

Shaved Parmesan (for serving)

1. Gently toss smoked trout, lemon zest, red pepper flakes, ¼ cup mixed herbs, and ¼ cup olive oil in a large bowl to combine; season with salt and black pepper. Let sit at room temperature 20 minutes.
2. Meanwhile, preheat oven to 350°. Drizzle both sides of bread with olive oil; season with salt. Toast on a rimmed baking sheet until golden brown and crisp, 8–10 minutes. Let cool, then crumble into small pieces. Set croutons aside.
3. Whisk egg yolk, garlic, and 1 tsp. lemon juice in a medium bowl to combine. Whisking constantly, gradually add vegetable oil and 2 Tbsp. olive oil, drop by drop at first, then in a steady drizzle; whisk until aioli is thickened and emulsified. Stir in 1 tsp. water to loosen sauce; season with salt.
4. Add kohlrabies and remaining 1 Tbsp. lemon juice to bowl with smoked trout mixture. Season with salt and pepper, drizzle with olive oil, and gently toss to combine.
5. Spread aioli on a large plate and top with kohlrabi salad, shaved Parmesan, reserved croutons, and remaining ¼ cup mixed herbs.
6. Do Ahead: Aioli can be made and trout marinated 1 day ahead. Cover and chill separately.