Preheat the oven to 375°F. Lightly grease a 9×13-inch baking dish.
Cook the penne according to the package directions until just al dente. Drain and set aside.
Heat the olive oil in a large skillet over medium heat. Add the garlic and cook for about 30 seconds, until fragrant.
Add the sun-dried tomatoes and spinach. Cook for 1–2 minutes, until the spinach begins to wilt.
Pour in the halal chicken broth and heavy cream. Stir in the Parmesan cheese, Italian seasoning, red pepper flakes if using, salt, and black pepper. Cook for 3–5 minutes, stirring frequently, until the sauce is creamy and slightly thickened.
Add the cooked chicken and pasta to the sauce and gently stir until evenly coated. Stir in 1 cup of the mozzarella.
Transfer the mixture to the prepared baking dish and sprinkle the remaining 1/2 cup mozzarella evenly over the top.
Bake uncovered for 20–25 minutes, until hot and bubbling and the cheese is melted. Let rest for 5 minutes before serving.

Chicken: Use fully cooked chicken, diced or shredded.

Pasta: Cook the penne just until al dente because it will continue cooking in the oven.

Sun-dried tomatoes: Drain excess oil before chopping for the best texture.

Sauce: If the sauce becomes too thick before assembling the casserole, stir in a small splash of chicken broth.

Red pepper flakes: Leave them out for a milder, family-friendly casserole.

Make ahead: Assemble the casserole, cover, and refrigerate until ready to bake. Add a few extra minutes to the baking time when cooking from cold.

Storage: Store leftovers in an airtight container in the refrigerator for 3–4 days.

Reheating: Reheat until thoroughly hot. A small splash of milk or cream can help restore the creamy texture.