Step 1

Preheat oven to 425F.

Step 2

Line a baking sheet with parchment paper (or lightly oil if necessary). Trim the ends of the squash, cut off the slender necks, and slice the necks in half, lengthwise. Then slice each squash into lengthwise slices, about 1/4 to 1/2-inch thick. Lay the slices on the cooking sheet in a single layer.

Step 3

Trim the ends of the onion and peel it. Cut it in half down through the top and place each half cut-side down on a cutting board. Slice into thin wedges. Separate the layers of the onions and sprinkle them over the squash.

Step 4

Bake for about 15 minutes, until bottoms of squash begin to brown. Sprinkle with pepper and salt, turn each slice over, and bake until bottoms of squash are browned, about 15 minutes more. Serve immediately, hot out of the oven.