Set aside a few sprigs of watercress and chop the rest roughly.
Add the chopped watercress and all the other ingredients into a food processor and whizz up to form a paste.
Cook the pasta following pack instructions then drain the water. Mix in the pesto and a glug more olive oil.
Optional: To bulk the dish, fry a broccoli (cut into florets) and a tin of butterbeans in olive oil in a small frying pan for about 5 minutes and add this to the pesto pasta. Combine well and heat gently before serving.
Serve topped with the sprigs of watercress which were set aside.