Set a cast iron or nonstick skillet over medium-high heat and add the water. Bring to a boil.
Add the ravioli and immediately cover with a lid. Steam until the pasta is tender, 5 to 6 minutes. It's ok if there's still some water in the skillet after steaming.
Pour in the mushroom sauce, and cook, stirring frequently until the sauce is thickened and coats the pasta, about 2 minutes.
Serve immediately, topped with Parmesan.
Notes
If it sticks--If your pasta sticks to the bottom of the skillet or pot, use a spatula to gently loosen it.
Storage & reheating--Store leftover ravioli in a sealed container in your fridge or cooler for up to 2 days. Reheat in a skillet over low heat, adding a splash of water or cream to loosen the sauce, if needed.