We had this discussion some weeks ago, and it emerged that there were some differences between British and American idioms to do with 'beans'. If you have found this expression in a British source, it will probably have the meaning that Paul has given ie full of energy. I think this comes from the idea that beans are a filling and nourishing food, so you will be full of energy if you have eaten a meal of beans. In the US, there are various expressions such as 'It ain't worth a hill of beans' which are used to describe something valueless and pointless. This is the source of Bruce's suggestion about foolish ideas.

If somebody is "full of beans, it means they have a lot of energy.

They might be addicted to Heinz! :))))

"Full---of---Beans" = Full----of----Confused---Ideas, or Full---of---Foolish---Ideas