Quinoa-and-Spinach Pilaf

In a large saucepan, melt butter over medium. Add onion and garlic; cook until soft, about 4 minutes. Add quinoa and cook 1 minute. Add water and bring to a boil. Reduce heat and simmer, covered, until water is absorbed, about 20 minutes. Stir in spinach and lemon zest, then season with salt and pepper.