Blanche the peas in boiling water for 2 minutes, then remove them with a slotted spoon. Rinse them immediately under cold water, then set aside.
Add the pasta to the boiling water and cook it following the instructions on the packaging.
Meanwhile, put the peas, garlic, cream cheese in a food processor and whiz, until you get a coarse paste.
Add a spoonful of the pasta’s cooking water, the lemon juice & zest, then whiz again, until you get a smooth sauce.
Add the cayenne and cider vinegar. Season with salt and pepper.
Drain the spaghetti, putting a cupful of the cooking water aside.
Put the spaghetti back in the saucepan, add the pea & rocket sauce and enough cooking water to mix the pasta easily with sauce.
Serve with plenty of freshly ground pepper.