Finely chop the shallot and garlic. Cut the mushrooms into fairly large pieces.
Bring a large pan of salted water to the boil. Add the tortellini and cook for 2–3 minutes, or according to the packet instructions. Transfer the tortellini to a plate with a slotted spoon, reserving the pasta cooking water.
Meanwhile, heat the olive oil in a large frying pan. Add the shallot and sauté for about 5 minutes until softened. Add the garlic and mushrooms and cook over low heat for about 5 minutes, until the mushrooms have softened and released their juices.
Add a splash of the reserved pasta water if the mixture seems too dry or sticky. Stir in the ricotta, lemon zest then gradually add a little more pasta water, stirring until you have a thick, smooth and silky sauce.
Add the lemon zest and season with salt and freshly ground black pepper to taste.
Turn off the heat and gently add the tortellini to the sauce. Toss carefully to coat without breaking the pasta.
Serve immediately with plenty of grated Parmesan or Pecorino and chopped fresh parsley.