I sprayed them with a little bit of olive oil. You can also use this method to evenly oil leafy greens like kale. I actually baked few batches. Maybe the type of the kale I had in my backyard has already salty flavor. When I added salt, the taste of the first batch was too salty for me. So in the latter batches, I sprinkled just a few pinches. I laid the pieces on a natural parchment paper on an oven tray.