Step 1: Sauté mirepoix. In a large non-stick skillet, heat olive oil over medium heat until hot but not smoking. Add the onion, carrots, and celery and sauté for 3 minutes, stirring occasionally.
Step 2: Add garlic. Add the garlic and cook, stirring frequently, for about 1 more minute.
Step 3: Slow cook. Spray the inside of your slow cooker with cooking spray. Add the whole chicken breasts, sautéed vegetables and garlic, beans, thyme, broth, bay leaves, seasoning salt, and pepper. *Do not add the spinach here. You'll add it at the end. Stir well and cook on high for 3 hours, or on Low for 5 hours or until 165 degrees F. Add the fresh spinach, stir to combine, and serve when wilted. I let it sit, covered, for about 5 minutes to soften the spinach.
Step 4: Shred chicken and serve. Carefully remove the chicken from the hot soup, let it cool a bit and then shred. Add the chicken back to the pot and give everything a good stir. Remove the bay leaves and serve garnished with fresh Parmesan, lemon wedges, and freshly chopped parsley, if desired. *Season with additional salt and pepper, to taste.