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, let stand covered for 5 minutes, then 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 - Sprinkle with dried thyme, salt, and pepper. If using spinach, add it now and cook until just wilted, 1 to 2 minutes.
06 - Add the cooked quinoa to the skillet. Drizzle with lemon juice and toss everything together until well combined and heated through.
07 - Remove from heat. Stir in fresh chopped parsley.
08 - Serve hot, garnished with grated Parmesan or vegan cheese and additional fresh parsley if desired.