Cook the pasta shells in a large saucepan of salted boiling water according to the packet instructions until al dente.
Meanwhile, heat the oil in a large frying pan, add the spring onions and cook over a medium heat for 2–3 minutes. Add the cheeses and stir while they blend into a smooth sauce.
Drain the pasta shells and transfer to a warmed serving bowl. Stir in the sauce and season to taste with salt and pepper. Sprinkle with the chives and serve immediately.