Season the chicken breasts with salt, black pepper, garlic powder, oregano, and thyme on both sides.
In the bottom of the crockpot, place the chopped onion and minced garlic. Drizzle with olive oil and mix lightly.
Place the seasoned chicken breasts on top of the onion and garlic mixture.
Pour the chicken broth over the chicken breasts, ensuring they are mostly submerged.
Cover the crockpot and cook on low for 6 hours, or until the chicken is tender and cooked through.
In the last 30 minutes of cooking, add the baby spinach and cherry tomatoes to the crockpot, stirring gently to combine.
Once done, remove the chicken from the crockpot and let it rest for a few minutes before slicing.
Serve the chicken on a platter surrounded by the onions, garlic, spinach, and tomatoes from the crockpot. Garnish with fresh parsley if desired.