In a shallow dish, combine the panko, Parmesan, and thyme. Season with salt and pepper. Dip each squash round into the panko mixture, coating it evenly on both sides, pressing the coating to stick. Place them in a single layer without touching on the prepared baking sheets. Spray lightly with nonstick cooking spray. Transfer to the oven and bake until golden brown and crispy, rotating top to bottom, about 25 minutes. Using a metal spatula, immediately remove the crisps to a rack to cool slightly (and to prevent them from becoming soggy) before serving.