Boil the pasta as per the packet instructions.
While waiting for the water to boil, chop the onion finely and sauté it until it becomes translucent.
Add the sausages crumbled or sliced (depending on how you prefer them), and brown them. If adding peperoncino, you can add it now. (I don't when cooking for my kids, as they start screaming and pawing at their mouths if they eat even a speck of chilli).
Add the tomato puree, spinach and salt and simmer on a low heat until the pasta is done, stirring occasionally.
Drain the pasta, add the sauce and stir.
Grate Pecorino over it and serve immediately.