Drain the cans of green beans and put them in a slow cooker.
In a small bowl, mix together cream of celery soup, milk, Worcestershire sauce, onion powder, garlic powder, and black pepper. Pour over the green beans and gently stir to coat.
Cover and cook on low for 4-5 hours or high for 3-4 hours, or until heated through.
Stir 1 cup of French fried onions into the green bean casserole. Top with the remaining French fried onion and serve.
Video
Notes
If you prefer to use the oven, bake it at 350°F for 30-35 minutes or until hot.