Preheat the oven to 425°F. Line two baking sheets with parchment paper.
Trim off the top and bottom of the squash, stand it on a flat end, and cut it in half. Scoop out the seeds with a spoon, then cut each half into slices about ⅜ to ½ inch thick.
In a small bowl, combine the garlic powder, salt, pepper, basil, thyme, oregano, and red pepper flakes.
Place the squash slices in a large mixing bowl and drizzle with the olive oil. Toss well with your hands until every piece is coated.
Sprinkle half of the Parmesan and half of the herb mixture over the squash and toss. Add the remaining Parmesan and herb mixture and toss again until the slices are evenly coated.
Divide the squash slices between the two baking sheets, arranging them in a single layer. Leave a little space between the slices and avoid overcrowding the sheets, or the squash will steam instead of roast and won’t get crisp.
Scrape up any Parmesan and herbs left in the bowl and sprinkle them over the slices.
Bake for 20 to 25 minutes, until the squash is tender and golden. If both sheets are in the oven at the same time, swap their positions halfway through baking so the slices brown evenly. There’s no need to flip the slices. The bottoms will come out darker and crispier than the tops.
Transfer the roasted acorn squash to a serving platter, garnish with fresh parsley, and enjoy!