In a microwave-safe bowl add the onions, flour, basil, garlic, tomato paste, and olive oil. Microwave for 5 minutes, stirring every 90 seconds or so.
Add broth, tomatoes, & chicken to the crockpot & stir.
Add the mixture from step 1 to the crockpot.
Season with sea salt, black pepper, & Italian seasoning. (I used Flavor God Italian Zest instead)
Stir & cover. Cook on LOW for 4-6 hours or on HIGH for 3-4 hours.
Use a fork to remove the chicken out of the crockpot. On a cutting board, shred or cut the chicken into bite-size pieces. Add the chicken back into the crockpot.
Add tortellini, spinach, & cheese.
Slowly pour the half & half in, stirring as you pour.
Put the lid back on and cook on HIGH for about 10 more minutes, or until the tortellini are cooked through.