Cut the baguette three-quarters of the way through lengthways, leaving the back intact. Hollow out some of the inside to make room for the filling.
Spread the whole baguette thinly with the butter and then the pesto.
Fill with layers of the ham, cheese, red peppers and lettuce then tie together with kitchen string at regular intervals - to keep all the filling inside. Cut into four to serve.
Cook's tip: If going on a picnic, wrap the baguette tightly in clingfilm or foil for transportation.