Heat oil in a large skillet over medium-high heat. Add mushrooms and cook until softened, about 5 minutes. Add red pepper flakes and spinach, cooking until spinach is wilted.
Stir in Ragu(R) Sauce and water. Bring to a boil. Stir in uncooked noodles. Reduce heat to medium and cook covered until noodles are tender, about 20 minutes. Note: be sure to stir frequently so the noodles do not settle at the bottom of the pan.
Top noodles with spoonfuls of ricotta cheese and then sprinkle with mozzarella cheese. Reduce heat to a simmer and cook covered until cheese is melted (about 5 minutes). Sprinkle with grated Parmesan cheese, if desired.