Sauté the aromatics & mushrooms: In a large ovenproof skillet (Ø 28–30 cm), heat the olive oil over medium heat. Add the onions, garlic, and mushrooms. Cook for a couple minutes, then season generously with salt, pepper, and Italian seasoning. Cook, stirring occasionally, until the mushrooms release their liquid and soften, about 7–8 minutes.
Add the spinach & liquids: Stir in the fresh spinach and let it wilt slightly. Pour in the broth and pasta sauce, then add the dry pasta and cherry tomatoes. Sprinkle in a pinch of red pepper flakes, if using. Stir well and bring to a gentle simmer.
Assemble the dish: Turn off the heat and dot the ricotta over the pasta mixture. Arrange the mozzarella slices evenly on top, then sprinkle with Parmesan.
Bake: Cover with a lid (or aluminum foil) and transfer to the oven. Bake for 25 minutes.
Broil & finish: Remove the lid and let the cheese turn golden, about 2–3 minutes under the broiler (optional).
Serve: Garnish with fresh parsley. Serve hot and enjoy!
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