Bring a pan of water to the boil and cook the pasta for 9-10 minutes until tender, adding in the peas for the last 2-3 minutes. Drain the pasta, reserving 75ml of the cooking liquid.
Return the pasta to the pan. Over a low heat, stir in the garlic and spinach and cook until the spinach is just beginning to wilt. Add in the crème fraîche, cheddar, lemon juice and prawns, along with the reserved cooking liquid. Stir until combined, then season and heat for a further minute. To serve, divide between four plates, then scatter the lemon zest on top.