In a medium saucepan, combine the rinsed quinoa and vegetable broth. Bring to a boil, then reduce the heat to low, cover, and simmer for about 15 minutes or until the quinoa is fluffy and the liquid is absorbed. Remove from heat and let it sit covered for 5 minutes. Fluff with a fork.

While the quinoa is cooking, heat the olive oil in a large skillet over medium heat. Add the diced onion and sauté for about 3-4 minutes until translucent.

Add the minced garlic and sliced mushrooms to the skillet. Cook for an additional 5-7 minutes, stirring occasionally, until the mushrooms are tender and browned.

Stir in the fresh spinach and dried thyme, cooking until the spinach is wilted, about 2-3 minutes. Season with salt and pepper to taste.

In a large bowl, combine the cooked quinoa with the sautéed spinach and mushroom mixture. Drizzle with lemon juice and toss gently to combine.

If desired, top with crumbled feta cheese and chopped walnuts for added flavor and texture.