to be honest to make it healthier you could not put all the whipped cream on top. I made banoffee pie for my food tech and because I don't like cream I just ommitted it, and I don't like the fact most banoffee pies have like one layer of chopped banana so you end up with caramelly toffee on biscuit with a ton of cream and hardly any banana taste so I mashed a lot of banana and mixed with the toffee. So it actually tasted like banoffee haha. Ok I started to go a bit off topic but yeah, omit the cream that'll reduce the calories and fat a lot.
Does it have to be biscuits? You could use bashed-up bran flakes or shreddies so you'd at least get some fibre and vitamins instead of just sugar and fat.