Cook the pasta in boiling water as instructed on the packet (usually just a few minutes). Add the peas for the final 2 minutes cooking time. Drain and rinse under cold water to cool, then drain again.
Grate the zest from the lemon and squeeze the juice into a bowl along with the olive oil and plenty of seasoning. Add the cooled pasta and peas and mix well. Cover and chill, spooning out portions as and when you want. (If you're keeping this for a little while, by days 3 and 4 you'll need to stir in a little more olive oil to loosen the pasta).