Meanwhile, combine 1 1/4 cups water, quinoa, and the remaining 1/4 teaspoon salt in a medium saucepan. Bring to a boil over medium-high heat. Reduce heat to medium-low, cover, and simmer until the quinoa is tender, 12 to 15 minutes. Remove from the heat and fluff the quinoa with a fork. Stir in spinach, cover, and let stand for 5 minutes.