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 cook until translucent, about 3 minutes. Add minced garlic and cook for 1 minute until fragrant.
03 - Add sliced mushrooms to the skillet. Cook, stirring occasionally, until mushrooms are golden brown and their liquid has evaporated, about 7 minutes.
04 - Stir in dried thyme, salt, and black pepper. Add baby spinach and cook until just wilted, 1 to 2 minutes.
05 - 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. Serve hot, garnished with grated Parmesan or vegan cheese and additional parsley if desired.