In a large skillet, heat olive oil over medium heat. Add the diced onion, garlic, carrots, and celery. Sauté for about 5 minutes until the vegetables are softened. Stir in the thyme, oregano, salt, and pepper.

Transfer the sautéed vegetables to a slow cooker. Pour in the chicken broth and add the chicken breasts. Cover and cook on low for 6-7 hours or high for 3-4 hours, until the chicken is cooked through.

Remove the chicken from the slow cooker and shred it with two forks. Return the shredded chicken to the slow cooker.

Stir in the heavy cream and potato gnocchi. Cover and cook on high for an additional 30 minutes, or until the gnocchi are tender.

Add the fresh spinach, parsley, and lemon juice just before serving. Stir until the spinach wilts, then ladle the soup into bowls.