01 -  Preheat oven to 375°F. Lightly grease a 9x9-inch baking dish with oil or butter. 
 02 -  Combine quinoa and vegetable broth in a medium saucepan. Bring to a boil, reduce heat, cover, and simmer for 15 minutes until liquid is absorbed. Fluff with a fork and set aside. 
 03 -  Heat olive oil in a large skillet over medium heat. Add chopped onion and sauté for 3 minutes until translucent. 
 04 -  Stir in minced garlic and sliced mushrooms. Cook for 6 to 7 minutes until mushrooms are soft and moisture has evaporated. Add spinach and sauté for 1 minute until wilted. Remove from heat. 
 05 -  Melt butter in a separate saucepan over medium heat. Whisk in flour and cook for 1 minute. Gradually add milk and heavy cream, whisking until the sauce thickens, about 3 to 4 minutes. 
 06 -  Remove pan from heat. Stir in Parmesan, nutmeg, salt, and black pepper until fully incorporated and smooth. 
 07 -  In a large mixing bowl, combine cooked quinoa, sautéed vegetables, and Alfredo sauce. Mix thoroughly to distribute ingredients evenly. 
 08 -  Transfer mixture into the prepared baking dish. Sprinkle mozzarella and additional Parmesan evenly over the surface. 
 09 -  Bake for 20 to 25 minutes until golden and bubbling. 
 10 -  Allow to rest for 5 minutes before serving. Garnish with chopped parsley if desired.