Kohlrabi Caesar Salad

Name: Kohlrabi Caesar Salad
Ingredients: 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)