Heat 1/2 tsp butter in a pan and fry the bacon until done, turning half way through. Drain on a paper towel and set aside.
To make the pesto put the watercress, parmesan, cashew nuts and salt into a food processor and whiz into a paste. Transfer to a container and mix as much olive oil as you want.
Assemble your sandwiches starting with the sandwich base, then pesto, bacon, peppers, sundried tomatoes, radishes, rocket and and sandwich top.