Slice the stem and blossom ends off the squash. Slice squash into ½” rings. Using a spoon, scoop out and discard the seeds from each ring.
Dip each squash ring in the melted butter, and season with salt and freshly ground black pepper. Saute squash in a skillet over medium heat or bake at 350º until the squash is tender and starting to brown.
Dress spinach with your favorite salad dressing. Top with the squash rings.