Bring a large pot of generously salted water to a boil. Cook the rigatoni until just shy of al dente, usually 1 to 2 minutes less than the package directions, then reserve about 1/2 cup pasta water and drain.

Heat 1 tablespoon olive oil in a large oven-safe skillet over medium-high heat. Add the mushrooms in a single layer and cook for 5 to 7 minutes, stirring occasionally, until browned and their moisture has evaporated.

Add the remaining tablespoon of olive oil and the diced onion. Cook for 3 to 4 minutes until softened, then add the garlic, Italian seasoning, kosher salt, and black pepper and cook for about 30 seconds.

Stir in the crushed tomatoes and water or low-sodium vegetable broth. Simmer the sauce for 5 minutes so the flavors begin to combine.

Add the baby spinach and cook for 1 to 2 minutes, just until wilted. Avoid cooking it longer than necessary so the spinach stays bright and does not release too much liquid.

Stir the drained rigatoni into the skillet sauce. If the mixture looks dry, add the reserved pasta water a few tablespoons at a time until the sauce coats the pasta generously.

Dollop the ricotta into the skillet and gently fold it through, leaving some creamy pockets visible. Stir in half of the mozzarella and half of the Parmesan.

Top the skillet with the remaining mozzarella and Parmesan. Bake at 400°F for 10 to 12 minutes until bubbling, then broil for 1 to 2 minutes if you want a more browned top, watching closely.

Let the rigatoni rest for 5 minutes before serving. Finish with chopped basil or parsley for a fresh, colorful garnish.