Cut the sausagemeat into small pieces and roll into walnut-sized meatballs.
Heat half the oil in a large nonstick frying pan, add the meatballs and cook over a medium heat, stirring frequently, for 10 minutes until cooked through. Remove from the pan with a slotted spoon.
Meanwhile, plunge the pasta into a large saucepan of lightly salted boiling water. Return to the boil and cook for 8 minutes. Add the peas, return to the boil and cook for a further 2 minutes until the peas are just tender and the pasta is al dente. Drain well, reserving 4 tablespoons of the cooking water.
Add the garlic, sage, chilli flakes and salt and pepper to taste to the meatball pan and cook over a low heat for 2–3 minutes until the garlic is soft but not browned. Return the meatballs to the pan.
Return the pasta and peas to the pan and stir in the meatball mixture, reserved cooking water and remaining oil and heat through for 2 minutes. Serve in bowls topped with grated Parmesan.