Saute chopped onion, celery and carrots in 2 Tbsp. of olive oil for 10 minutes (on stove, medium heat). Put this mixture in the crockpot.
You can either cut up the chicken breasts or leave them whole, add them to the crockpot. Add the frozen green beans, water, boullion, basil and ground black pepper. Cook in the crockpot on low for 10 hours (or on high for 5-6 hours)