Preheat the oven to 425°F and line two baking sheets with parchment paper.

Lightly drizzle the acorn squash halves with olive oil, sprinkle with salt, and rub with your hands to coat. Place cut side down on one of the baking sheets and roast for 25 to 40 minutes, or until fork-tender. The exact timing will depend on the size of your squash.

Place the mushrooms and sage on one side of the second baking sheet and the onions on the other side. Drizzle both sides with olive oil and sprinkle with salt and pepper. Toss to coat and spread evenly on the baking sheet. Roast for 18 to 23 minutes, or until the onions and mushrooms are tender and browned around the edges.

Meanwhile, make the dressing: In a medium bowl or liquid measuring cup, whisk together the apple cider vinegar, maple syrup, garlic, salt, mustard, and several grinds of pepper. Drizzle in the olive oil while whisking and continue to whisk until the dressing is emulsified.

Make the filling. In a large bowl, toss together the cooked rice, roasted mushrooms and onions, apple, feta, parsley, cranberries, pecans, pepitas, and salt. Add half the dressing and toss to coat.

While the squash is still warm, brush the orange flesh with more of the dressing and season with salt and pepper. Fill with the rice mixture and garnish with sage. Serve with the remaining dressing on the side.