Preheat your oven to 400°F (200°C).

In a medium pot, bring water to a boil and add the cubed butternut squash. Cook for about 10 minutes or until the cubes are tender when pierced with a fork. Once cooked, drain the squash and set it aside.

In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add the finely chopped onion and sauté for 3-4 minutes, or until the onion becomes translucent and fragrant.

Stir in the minced garlic along with the dried sage, thyme, salt, and black pepper. Cook for an additional minute.

Incorporate the cooked quinoa, butternut squash, dried cranberries, and chopped walnuts into the skillet. Mix thoroughly until all ingredients are evenly combined and heated through, about 2-3 minutes. Remove from heat.

Brush each portobello mushroom with the remaining tablespoon of olive oil and place them on a baking sheet with the gill sides facing up.

Generously spoon the quinoa mixture into each portobello mushroom cap, pressing lightly to pack the filling in.

If desired, sprinkle the crumbled feta cheese over the top of the stuffed mushrooms.

Place the baking sheet in your preheated oven and bake for 20-25 minutes, until tender and the tops are golden brown.

After baking, remove the mushrooms from the oven and let them cool slightly. Garnish with fresh parsley and serve warm.