How to Make It
Heat oven to 400° F. Toss the bread, 2 tablespoons of the oil, and a pinch each salt and pepper on a rimmed baking sheet. Bake until crisp, 10 to 15 minutes. Let cool.
Toss together the kale, onions, soaking liquid, the remaining 2 tablespoons of oil, ½ teaspoon salt, and ¼ teaspoon pepper. Let sit, tossing occasionally, until slightly softened, 10 to 15 minutes. Add the spring greens, Parmesan, and croutons and toss to combine.