Preheat the oven to 425°F.
After washing the squash, cut it in half. Remove any stringy flesh and seeds using a spoon. Place the squash, skin side down, on a baking sheet lined with parchment paper.
Melt the butter and mix it with the miso, vinegar, and maple syrup. Whisk everything together until it's smooth. Brush the squash with the butter mixture.
Roast for 25 minutes, or until the squash is fork-tender.
Take out the squash from the oven and sprinkle it with parsley and sesame seeds. Serve right away.