Preheat the Oven:

• Preheat your oven to 375°F (190°C).

Cook the Pasta:

• Cook the penne pasta in salted water according to the package instructions until al dente.
• Drain and set aside.

Prepare the Chicken and Vegetables:

• Heat a drizzle of vegetable oil in a large skillet over medium heat.
• Add the finely chopped onion and minced garlic. Sauté for about 3 minutes until the onion is translucent and fragrant.
• Add the chicken pieces, season with salt and ground black pepper, and cook until the chicken is no longer pink.
• Add the chopped sweet pepper and cook for another 3-4 minutes, until softened.

Add the Tomato Sauce:

• Pour the tomato sauce into the skillet with the chicken and vegetables.
• Stir well and let it simmer for 5 minutes.
• Remove from heat.

Make the Creamy Sauce:

• In a saucepan, melt the butter over medium heat.
• Stir in the flour and cook for 1-2 minutes to create a roux.
• Gradually whisk in the milk, stirring constantly to prevent lumps.
• Cook until the sauce thickens, then season with a pinch of salt and black pepper.

Combine Ingredients:

• In a large mixing bowl, combine the cooked pasta, chicken and vegetable mixture, and creamy sauce.
• Stir until everything is well coated.

Assemble the Pasta Bake:

• Grease a baking dish with cooking spray or vegetable oil.
• Pour the pasta mixture into the dish and spread it out evenly.
• Sprinkle shredded mozzarella cheese over the top.

Bake:

• Bake in the preheated oven for 20-25 minutes, or until the cheese is melted and golden brown.

Let It Rest and Serve:

• Remove the pasta bake from the oven and let it rest for 5-10 minutes before serving.
• Garnish with fresh parsley or basil if desired.