Preheat the oven to 375°F (190°C) and line a baking sheet with parchment paper.

Clean each portobello mushroom under cool running water and pat dry. Remove stems and gills to create stuffing space. Brush caps with olive oil, then sprinkle with salt and pepper.

In a saucepan, combine quinoa and vegetable broth. Bring to a boil, then reduce to a simmer and cover, cooking for about 15 minutes until fluffy.

In a skillet, heat olive oil and sauté diced butternut squash for about 10 minutes. Add garlic and thyme in the final minute.

In a bowl, combine cooked quinoa, sautéed squash, cranberries, and walnuts until well mixed.

Spoon the stuffing mixture into each portobello cap, filling generously without overcrowding.

Top each stuffed mushroom with Parmesan cheese, then bake for 20-25 minutes until tender.

Remove from oven and let cool slightly before serving.