Heat a Dutch oven or large soup pot over medium heat. Add the olive oil.
Season the chicken breasts with salt, pepper, garlic powder, and onion powder. Add them to the pot and brown on both sides.
Add the minced garlic and stir for 30 seconds.
Pour in the chicken broth. Add the onion, carrots, celery, oregano, and bay leaf.
Bring the soup to a boil, then reduce the heat. Cover and simmer for 20 minutes, or until the chicken is cooked through.
Remove the chicken and bay leaf from the pot. Discard the bay leaf.
Shred the chicken and set aside.
Add the cheese tortellini to the broth and cook according to the package directions.
During the last minute of cooking, stir in the spinach and shredded chicken.
Stir in the reduced-fat shredded cheese until melted.
Slowly stir in the fat-free half-and-half. Heat until warmed through, then serve.