I'm sure loads of people on here feed carrots both frozen and fresh.
And I am sure people stuff kongs with bananas before freezing them.
But I would make sure your springer liked bananas first.
My springer just chews them and spreads the mess of the carpet and will spit bananas out after a few chews.
Not too sure about the amount though. Perhaps just two per day cos I am not sure how well they digest them. My old sprollie Hamish seems to poo most of his out.
My previous springers used to love fresh peas, pod and all, beetroot and turnip. They also used to raid the strawberry patch.
But I am sure a better expert will come along tomorrow.