For the pesto, combine all the ingredients to make a paste. Season to taste with salt and pepper.
Wash the spring onions and cut 5mm strips. Heat olive oil in a frying pan, add spring onions and peas and fry over medium heat for 10 minutes, stirring occasionally.
Add the vegetable stock and 100g of pesto and bring to the boil and then simmer for 5 minutes. Season to taste with salt and pepper.
In the meantime, boil the penne in salted water until al dente, drain well and add to the sauce. Let everything simmer again briefly and serve.
