Brush a little oil over each sausage, then cook under a preheated medium grill for 15 minutes or until golden and cooked through. Cool slightly, then cut into bite-sized pieces.
Meanwhile, heat the remaining oil in a pan, add the onion and cook for 10 minutes until softened. Stir in the mustard and stock and simmer for 5 minutes, then stir in the crème fraîche and lemon juice and most of the rind.
While the sausages and sauce are cooking, cook the pasta in a large saucepan of salted boiling water according to the pack instructions until al dente. Drain, reserving a little of the cooking water, and return to the pan. Stir through the sausages and sauce, adding a little cooking water to loosen if needed.
Spoon into serving bowls and serve sprinkled with the parsley and the remaining lemon rind.