If using frozen green beans, run under warm water in a colander for a few minutes and then let drain while assembling the rest of the ingredients.
If using fresh green beans, break them into bite-sized pieces and wash thoroughly in a colander and let drain.
Add all of the ingredients, except the green beans, half the bacon, and half the fried onions to the slow cooker and mix well.
Once the green beans have drained, add them to the mixture in the slow cooker and mix together.
Cover slow cooker and turn heat on. Cook on low for 6 hours or on high for 4 hours.
After 4 hours of cook time on high (6 hours on low), check for doneness by tasting one of the beans. If tender, then the beans are done. Turn temperature to warm and leave the lid off for 15-20 minutes to allow some evaporation of some of the liquid.
If serving directly from the slow cooker, add the rest of the fried onions and bacon to the top of the casserole.
If serving in a serving dish for the table, remove the green bean casserole to the serving dish before topping with bacon and fried onions.
Serve alongside your Thanksgiving dinner or any dinner of the week. Will keep up to 5 days in the refrigerator.