Place onion, tomato paste, garlic, olive oil, oregano, salt, and pepper flakes in a large microwave safe bowl.
Microwave for 3 minutes, then stir, to combine everything really well, and return to the microwave for an additional 2-5 minutes, until onion is softened. Stir well.
Pour the bowl’s contents into an oval, 5-7 quart slow cooker
Stir heavy cream into the contents in the slow cooker.
Trim chicken breasts, and pound to even thickness, then season with salt, pepper, and paprika, on all sides.
Set chicken into sauce in slow cooker, arranging in an even layer.
Cover slow cooker, and cook on low for 1-2 hours, checking chicken after about 45 minutes to read temperature. Cook until chicken reaches 160 degrees F. *Use an instant read thermometer to get the chicken cooked perfectly.
Once chicken reaches 160 degrees F, sprinkle parmesan cheese over the top of the chicken, and recover with lid.
Cook an additional 5-10 minutes to allow the chicken to come up to 165 degrees F and for the parmesan cheese to melt.
Serve sprinkled with fresh basil, and plenty of sauce. Wonderful served with pasta.