In a 3-quart sauté pan or large skillet, heat 3 tablespoons of butter over medium heat. When butter shimmers, add the mushrooms, and cook undisturbed for 5 minutes. Season with salt to taste, stir, and continue cooking until the mushrooms are tender and browned, stirring occasionally, about 5 minutes. Remove to a plate with a slotted spoon.
3 tbsp unsalted butter, 8 oz mushrooms
Increase the heat to medium-high and add remaining butter. When butter shimmers, add chicken, season with salt and pepper to taste, and cook until lightly browned, stirring occasionally, about 10 minutes.
3 tbsp unsalted butter, 1 lbs chicken breast
Stir in quinoa, broth, bay leaf, and salt and pepper, to taste. Bring to a boil. Reduce heat to low and simmer, partially covered, about 17 minutes. You want quinoa to be completely tender and most of the liquid absorbed.
1 cup quinoa, 1 ¾ cup vegetable broth, 1 dried bay leaf
When quinoa is tender, discard the bay leaf and add the spinach. Cover the pan and let the spinach cook for about 2 minutes or until wilted. Then using a pair of tongs, toss the spinach with the quinoa and chicken.
6 oz baby spinach leaves
Stir in mushrooms and mustard sauce. Serve garnished with parsley and red pepper flakes, if desired.
parsley and red pepper flakes