Bring a large pot of salted water to a boil. Add the penne pasta and cook according to package instructions until al dente, about 9-11 minutes. Drain the pasta in a colander and set aside. Reserve about 1/2 cup of pasta water to adjust the sauce later if needed.
Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add the diced chicken breast, season with salt and pepper, and cook for about 5-7 minutes until browned and cooked through. Remove the chicken from the pan and set aside.
In the same skillet, add the remaining tablespoon of olive oil. Toss in the peeled and deveined shrimp, seasoning lightly with salt and pepper. Cook for 2-3 minutes on each side, until the shrimp turn pink and are opaque. Remove the shrimp and set aside with the chicken.
Reduce the heat to medium and add the minced garlic to the skillet. Sauté for about 1 minute until fragrant but not browned. Pour in the chicken broth and stir, scraping up any browned bits from the bottom of the pan. Let it simmer for 2-3 minutes to reduce slightly.
Slowly stir in the heavy cream and Italian seasoning. Let the sauce simmer gently for 3-4 minutes until it thickens. Taste and adjust salt and pepper as needed.
Return the cooked chicken and shrimp to the skillet. Add the drained penne pasta and toss everything together until the pasta is well coated in the creamy garlic sauce. Stir in the grated Parmesan cheese until melted and smooth. If the sauce seems too thick, add a splash of the reserved pasta water to loosen it.
Sprinkle freshly chopped parsley over the top for color and freshness. Serve immediately with a side of crusty bread or a light salad for a complete meal.