In a large pot or Dutch oven, heat the olive oil over medium heat. Add the diced onion and garlic and sauté for about 3 minutes, until the onion becomes translucent.
Add the diced carrots, celery, and bell pepper to the pot. Cook for another 5-7 minutes, stirring occasionally, until the vegetables soften.
Season the mixture with salt, pepper, dried thyme, and dried basil. Stir well.
Place the chicken breasts into the pot and pour in the chicken broth. Bring the mixture to a boil.
Once boiling, reduce the heat to a simmer and cook for 15 minutes until the chicken is cooked through.
Remove the chicken from the pot, shred it with two forks, and return it to the soup.
Stir in the pearl couscous and let the soup simmer for another 10-12 minutes, or until the couscous is tender.
Add the chopped spinach and lemon juice, stirring to combine. Allow to cook for another 2 minutes until the spinach wilts.
Taste and adjust seasoning if necessary. Serve hot, garnished with fresh parsley.