Bring a large pot of salted water to a boil. Add 12 oz rigatoni and cook according to package instructions until al dente. Drain well and set aside, reserving about 1/4 cup of pasta water for the sauce.
In a large skillet, heat 1 tablespoon olive oil over medium heat. Add the diced onion and cook for 3-4 minutes until translucent and soft. Stir in the minced garlic and cook for an additional 1 minute until fragrant.
Add the sliced mushrooms to the skillet. Cook for 6-8 minutes, stirring occasionally, until they release their moisture and begin to brown.
Sprinkle in 1 teaspoon dried oregano and 1 teaspoon dried basil. Stir to combine. Pour in 1 cup vegetable broth and bring to a simmer. Allow the mixture to reduce slightly, around 5 minutes.
Add the chopped fresh spinach and cook for 2-3 minutes until wilted.
Add the cooked rigatoni to the skillet. Toss everything together, adding reserved pasta water a little at a time if the sauce needs loosening. Season with salt and pepper to taste.
Remove from heat and stir in 1/2 cup grated Parmesan cheese. Serve hot, garnished with extra Parmesan if desired.
