01 - Bring vegetable broth to a boil in a medium saucepan. Add quinoa, reduce heat to low, cover, and simmer for 15 minutes until liquid is absorbed. Remove from heat and let stand, covered, for 5 minutes. Fluff with a fork.
02 - Heat olive oil in a large skillet over medium-high heat. Add chopped onion and sauté until translucent, approximately 3 minutes.
03 - Stir in minced garlic and cook for 1 minute until fragrant, being careful not to burn.
04 - Add sliced mushrooms to the skillet and cook, stirring occasionally, until golden brown and their liquid has evaporated, about 7 minutes.
05 - Add dried thyme, salt, and black pepper. If using spinach, stir in and cook until just wilted, 1 to 2 minutes.
06 - Add cooked quinoa to the skillet. Drizzle with lemon juice and toss everything together until well combined and heated through. Remove from heat and stir in fresh parsley.
07 - Serve hot, garnished with grated Parmesan or vegan cheese and additional fresh parsley if desired.