Let’s dive into the cooking process, reminiscent of the warmth and flavors of my grandmother’s kitchen:

1. Preheat your oven to 350°F (175°C). Grease a large baking dish and set aside.
2. Cook the spaghetti in a large pot of salted boiling water until al dente. Drain and set aside.
3. In a large skillet, heat olive oil over medium heat. Add the cubed chicken, season with salt and pepper, and cook until browned and cooked through, about 7-8 minutes. Remove from the skillet and set aside.
4. In the same skillet, add the onion and garlic, sautéing until translucent and fragrant, about 4 minutes.
5. Add the mushrooms to the skillet and cook until they release their moisture and are browned, about 5 minutes.
6. Sprinkle the flour over the vegetables, stirring to coat, and cook for 1 minute.
7. Gradually whisk in the chicken broth and bring to a simmer, allowing the sauce to thicken slightly.
8. Stir in the heavy cream, then add the cooked chicken back into the skillet, mixing well.
9. Combine the chicken mixture with the cooked spaghetti and half of the Parmesan cheese. Stir to combine everything evenly.
10. Pour the mixture into the prepared baking dish. Sprinkle with the remaining Parmesan and mozzarella cheese.
11. Bake in the preheated oven for 25-30 minutes, or until the top is golden and bubbly.
12. Remove from the oven and let cool for a few minutes. Garnish with chopped parsley before serving.