Preheat your oven to 375°F (190°C).
Prepare the pumpkins by cutting off the tops and scooping out the seeds.
In a saucepan, combine quinoa and vegetable broth. Bring to a boil, then reduce to simmer and cover for 15 minutes, or until liquid is absorbed.
In a skillet, heat olive oil over medium heat. Sauté the onion, garlic, and mushrooms until softened, about 5-7 minutes.
Add the cooked quinoa, chopped sage, and Parmesan to the skillet, mixing thoroughly to combine.
Season the mixture with salt and pepper to taste, then gently stuff the pumpkins with the filling.
Place the stuffed pumpkins in a baking dish, add a splash of water to the bottom, and cover with foil before baking for 30 minutes.
Remove the foil and bake for an additional 15-20 minutes to allow the tops to brown slightly.
Remove from the oven and allow to cool slightly before serving.