Source: http://allrecipes.com/recipe/229809/slow-cooker-green-bean-casserole/                    
                            
                        
                     
                    
                 
               
             
    
            
                
                    
Ingredients
                
                2 (16 ounce) packages frozen cut green beans
1 (10.75 ounce) can of cream of chicken
1 (10.75 ounce) can of cream of mushroom
2/3 cup milk
1/2 cup grated Parmesan cheese
1/4 tsp salt
1/4 tsp ground black pepper
1 (6 ounce) can French-friend onions, divided
             
      
            
                
                    
Instructions
                
                1.  Combine green beans, cream of chicken soup, milk, Parmesan cheese, salt, black pepper, and half the can of French-fried onions in a slow cooker.
2.  Cover and cook on Low for 5 to 6 hours. Top casserole with remaining French-fried onions to serve.