In a large pot, heat the olive oil over medium heat. Add the chopped onion, carrot, and celery, and sauté for about 5 minutes, until they begin to soften. Stir in the minced garlic and cook for another minute, just until it becomes fragrant.

Add the chicken pieces to the pot, seasoning them with a pinch of salt and pepper. Cook the chicken for 5-7 minutes, stirring occasionally, until the pieces are browned on all sides.

Rinse the quinoa thoroughly under cold water to remove any bitterness. Add the quinoa to the pot, followed by the chicken broth, thyme, and bay leaf. Bring the mixture to a boil, then reduce the heat to low, covering the pot and letting it simmer for about 20 minutes. The quinoa should be tender, and the chicken fully cooked.

Once the quinoa is cooked, remove the bay leaf and stir in the lemon juice, spinach, and fresh parsley. Allow the soup to cook for an additional 2-3 minutes, just until the spinach wilts. Taste the soup and adjust the seasoning with more salt, pepper, or lemon juice as needed.

Ladle the soup into bowls, and enjoy it piping hot!